Nuclear energy is powerful, badly misunderstood and might prove useful in combating global warming
, if people could just stop being pointlessly afraid of it.
The main lingering problem of nuclear energy is that it's associated with nuclear warfare and wastes and potentially deadly radiation. As a consequence, it suffers not only from weak public support but also outright opposition. Much of this is caused by an international and quite successful anti-nuclear movement, which was one of the major driving forces behind nuclear arms reduction treaties, but has nowadays degenerated into pseudoscience and fear-mongering.
See the FAQ on radioactivity and nuclear technology
for answers to the most important questions on this subject.