The question about what kinds of energy we use and why we use them is very much a political question more than it is a scientific one. Science can only comment on the facts of energy production.

The reality is that humans require energy. We need energy for heat, to cook, for transportation, and to run all of our technological equipment. So, producing energy is absolutely necessary. Right now, about 86% of the energy used commercially in the United States comes from fossil fuels. These fuels are very harmful to the environment and dangerous to work with. For example, mining coal is very destructive, causing extreme damage to ecosystems and producing toxic wastes that contaminate our water supplies. The burning of fossil fuels produces air pollution, including large quantities of CO2, which is a major concern because of its role in global warming. Use of fossil fuels as an energy source is also very inefficient, with most of the energy present in the fuel being wasted as heat rather than turned into useable energy.

Currently, only about 6.5% of the energy being used commercially in the United States comes from nuclear energy. However, in many ways nuclear energy is far superior to fossil fuels. Nuclear energy produces no greenhouse gases, and an 8.5g pellet of uranium can provide as much energy as burning one ton of coal. The main problem with nuclear energy is that it produces radioactive waste. This raises concerns about radioactive pollution escaping into the environment. People are also concerned about the possibility of having a nuclear accident that could cause radioactive contamination to escape, or of terrorists or other groups deliberately causing such a problem.

It is part of human nature that people are often simply more comfortable with things they are familiar with, and are suspicious or fearful of things that they are not. For example, people are sometimes afraid of being struck by lightning or eaten by a shark, even though the chances of such a thing happening are very remote. They will then smoke cigarettes and drive cars without a seat belt even though these habits are thousands of times more dangerous and present a very real and significant risk to their health and safety. A similar situation occurs with how people perceive nuclear energy. Some concerns that people have over nuclear power are not justified. For example, people sometimes think that a nuclear power plant could explode like a nuclear bomb, but this is not actually possible. In terms of energy production, because coal has been around a long time and is something that is encountered frequently, people are comfortable with it. In contrast, nuclear energy is something far more technologically complex and mysterious, and so oftentimes people view it with suspicion and as something that is very dangerous. The reality, though, is that estimates suggest that around 10,000 people die every year as a direct result of the normal coal-producing and burning industry, whereas there are no known deaths have every occurred from normal use of nuclear energy!

Nuclear energy is not a perfect energy source, and certainly concerns of radioactive contamination and accidents are legitimate ones. However, many people do view nuclear power as a safer, more efficient, and less polluting alternative to fossil fuels, and they would disagree with the assumption in your question that it is something that is very dangerous. However, the decision on which energy sources to invest in and use is ultimately one that is made by governments based on many different factors, of which safety, the environment, cost, public opinion, and international policy are only a few!

Nuclear energy is produced in nuclear power plants, where the radioactive reactions that produce energy are highly controlled and contained. As long as these controlled environments are functioning properly, and the waste of the reactions is properly contained, nuclear energy is not harmful. In fact, many people say that nuclear energy is much more environmentally friendly than the alternative (and more widely used) fossil-fuel routes of energy production, because the controlled nuclear reactions produce much less harmful gases than reactions of fossil fuels. However, this topic is highly debated and controversial. Some people think that nuclear energy is a bad idea because of the RISK for it to be harmful: if the special contained reaction environments malfunction, or if the nuclear waste cannot be contained forever, then there does exist potential for environmental damage. People who support the use of nuclear energy say that the risks are small and that this form of energy is becoming safer with newly developing technologies.

Do you think that nuclear energy is harmful or helpful? Because there is no definite answer, you can read more about nuclear energy and decide what you think! Your opinion will be as important as any one else's. In any case, currently nuclear energy is used to provide ~7% of the worlds energy and about ~16% of the worlds electricity.