I doubt if people like Elon Musk are “great demons”. We have to know what is materially great.
You are getting your food because of your karma. Your body is ādiātmika, the food is ādibhautika, and the demigods are ādidaivika. In modern science, only two things are recognized–your body and the food–but how some food enters some body is controlled by demigods based on your past good and bad deeds. There is an objective definition of “good” and “bad”, namely if one performs one’s duties as laid out by instructions of Lord Vishnu (e.g. the Varnashrama system) then it is good. But if one violates this system of duties, then it is called bad. This is the divine system of morality.
Demons are those people who create an alternative system of morality. In short, they change the definition of good and bad. But, this alone will not work unless they can also change the natural system of reward and punishment. If we arbitrarily change our definition of good and bad, nature will still punish us, because we are governed by the divine definitions of good and bad. So, it is not enough to merely change our definitions of good and bad, but also to alter the system of reward and punishment based on the new definition. Great demons can not only create an alternative system of morality, but they also have the power to change the system of reward and punishment.
Hence, in Vedic cosmology, there are two parts of the universe–upper and lower. The upper part of the universe is controlled by the divine system of morality (i.e., the definition of good and bad based on the instructions of Lord Vishnu), and the lower part of the universe is governed by the demoniac system of morality (which is completely contrary to the instructions of Lord Vishnu).
For example, in the divine system of morality, activities like intoxication, meat-eating, illicit sex, and gambling are punished. But in the demoniac system of morality, these activities are rewarded. Conversely, activities like charity and sacrifice are rewarded in the divine system, but they are punished in the demoniac system. For instance, you can imagine a government that levies extra taxes on you if you gave some money to charity; their reasoning would be: If you have got extra money to give in charity, then we want to take away that money so that you cannot perform charity. So, this kind of taxation would be an example of how charity and sacrifice can be punished. Similarly, if a husband and wife were chaste to each other, they would be thrown out of their social system. Conversely, those men and women who are willingly promiscuous would be welcome.
Now, we have to understand that the earthly planetary system is a part of the “upper half” of the universe. It is the lowest in the upper half, so living entities here don’t have control over the system of reward and punishment. But the system of morality is indeed divine. Conversely, the system of morality in the lower planetary systems is demoniac. In short, if someone performs sinful activities in this planet, then they will be punished. If they are really interested in performing sinful activities, then they ought to go to the world of alternative morality, i.e., the planets of the demons.
So, on the earthly planetary system, “great” demons cannot exist because “greatness” is defined by the ability to change the definition of good and bad, and then alter the natural system of reward and punishment. This is not possible on the earthly planetary system because it is controlled by demigods. There are, of course, rare occasions in which demons like Ravana usurp the demigods and then enforce their alternative system of morality even on earth. Then, Lord Vishnu appears to kill these demons and return the power to the demigods. But that is not the situation presently.
What we see as demoniac activity presently is some people trying to change the system of morality by manipulating the governmental laws, without the power to change nature’s laws. All their actions are subject to punishment because that is not permitted on the earthly planetary system. But such “demons” are enjoying their demoniac morality in this age, based on their good karma. When their karma is finished, then they will lose their power. However, they may be replaced by other demons, who will also enjoy their good karma for some time. Ultimately, they are punished.
Now, we can come to an understanding of science. What is science? It is understanding of the laws of nature, or how we can get what we want by our actions. Modern materialistic science is not truly a science, because it has no understanding of morality and the natural system of reward and punishment. And those who are playing with nature are not in control of nature; nature controls them. If true science is established, then morality is part of that science. Cause and effect are not enough in this true science; there are also consequences of our actions. In present science, there are only causes and effects, no consequences. So, presenting Vedic science means presenting a science of cause, effect, and consequence, based on a definition of good and bad, based on what is ordained by Lord Vishnu, and administered by the demigods as part of the upper planetary systems.
Our definition of science is different than modern science. If this science is understood, then the consequences of actions are part of science; the existence of God and demigods is part of science, and the transmigration of the soul based on its previous actions is also part of the same science. If any aspect of this science is not understood, then the whole thing is not understood. So, in presenting Vedic science, we do not separate soul, God, and matter; we present them collectively. Similarly, anyone who tries to present a “science” of matter in isolation can never succeed.
There are many people at present who want to study matter in isolation based on Vedic scriptures, and they think that they can just try to create advanced material technology without worrying about the soul, God, morality, and karma. These people will never succeed. Every single Vedic text discusses matter, soul, and God collectively. This is not by accident. We cannot understand matter without understanding the soul, the Supreme Soul, and the relation between them. For example, in the Bhagavad-Gita, the nature of the soul, the nature of matter, the nature of God, and the process of happiness are discussed collectively. The level of detail may change, but there is no Vedic text that only discusses only matter. Even astrology texts (e.g. Brihat Parashara Hora) begin by offering obeisances to Lord Vishnu, then describe the process of creation, the elements of nature, and which demigods rule over which elements. Similarly, all philosophy texts discuss everything collectively.
The main point is that Vedic science is a theistic science, but it can be transformed into an atheistic science only if the definition of good and bad is changed, along with the laws of nature. This is possible because laws of nature are controlled by personalities, and they are not impersonal. In short, the same laws don’t apply everywhere. But on this planetary system, the divine laws apply. So, what I am trying to present is also this combined philosophy of matter, soul, God, and karma.
Now, there are many hurdles in this process, and the biggest initial hurdle is that people are not intelligent enough to understand how the body is created based on the mind. Accordingly, they also cannot understand that to control matter we don’t need machines; we need the ability to chant mantras. By chanting a mantra, you can instruct matter to behave differently. This science of mantra chanting is based on the same principle as the creation of the body based on the mind. This process requires immense mental control. For example, you cannot think anything else while chanting the mantra; if the mind is disturbed, then that mantra will have no effect. Attaining that mental purity and power itself requires many lifetimes of practice. And only those people who have been purified in this way would be able to control matter mentally by the process of mantra chanting. This class of people was formerly called Brahmanas. Not the caste Brahmana, but the real Brahmana.
At the present, there are no Brahmanas. Only some people wearing a thread call themselves Brahmana. But they have no power; they don’t know anything; they are as ignorant as everyone else. By presenting this philosophy, if some intelligent people become interested, then by gradual purification they will acquire this power to control nature. For everyone else, this will just seem magic. To explain why this is not magic, but science, we can present all this philosophy and science. But just knowing the theory doesn’t mean that we can practice it to produce an effect.
For example, many people may know about the Hare Krishna mantra presently, but practically no one is chanting the mantra purely and perfectly. Most people are not even trying to perfect their chanting; they are just busy with some superficial things. So, knowing the mantra theoretically doesn’t mean we can attain bliss by chanting. Similarly, knowing the theory of matter doesn’t mean we can develop technology with it. Hence, there is a distinction between jnana and vigyana. The term jnana means theoretical knowledge, and the term vigyana means realized knowledge. That realization is a long and difficult process after we understand the theoretical knowledge.
The demons who acquired this power in the past performed severe austerities. For example, Hiranyakasipu sat in meditation for so long that his entire body was eaten up by ants. Now compare this situation to our present situation. Imagine that a mosquito bites you while chanting. It is very likely that you will forget about chanting and try to shoo away the mosquito. But not Hiranyakasipu. He was so absorbed in his meditation, that he was unmoved even when his entire body was eaten up by ants. So, we cannot compare these demons with ordinary people today. They were extraordinary personalities. Due to this extraordinariness, Lord Vishnu has to appear to kill them. For ordinary people, some mosquitoes will be sufficient to distract and disturb their meditation process.
Your question basically trivializes the problem at so many levels. First, this is not a science of matter alone; it involves soul, God, karma, and morality. Second, this science can only be understood either by an extraordinary intelligence (that practically nobody has at the present) or by the grace of the Lord. Third, even if it is understood, it cannot be practiced by everyone; it can be practiced by only those who have gained perfect mental control. Fourth, obtaining this mental control is not easy; it either requires extraordinary austerities (which ordinary people cannot perform) or pure devotion to the Lord. Therefore, only those who are devoted to Lord Vishnu, can by His grace understand this science theoretically and then obtain the mental prowess to practice it. Nobody else can.
The demons you are talking about are impossible in this age. People at the present are foolish, weak, lazy, and scared. So, by their effort, they cannot get anything. But by the grace of Lord Vishnu, it is possible. He will grant His grace if we become devotees. And devotees will not misuse this science. In fact, only devotees will be able to understand, practice, and present this kind of science.
So, there is nothing to worry about some so-called demon creating problems. The greatest worry is that we will fail in the mission of our life by wasting our time thinking about irrelevant things.