This gets linked a lot, but it is really good: The Edge
What is your dangerous idea? An idea you think about (not necessarily one you originated) that is dangerous not because it is assumed to be false, but because it might be true?
I didn’t read all the answers, but some of scientists I know. Let’s take Richard Dawkins. His dangerous idea is brilliant: That everything lies within our genes; that one day we will find out that people commit crimes because that is imprinted in there genes. His short article on this subject is brilliantly written as always (John Cleese in in there). Read for yourselves! I can only say Dawkins always awes me. The sheer amount of ingenious ideas combined with his way of communicating them makes him a genius.
Paul Davies says the fight against global warming is lost and hopeless. I agree. It is to be fought nevertheless.
Brian Greene talks about the multiverse idea. Freeman Dyson envisions the Biotechnology-revolution. Jordan Pollack thinks that Science maybe just another religion. Ray Kurzweil thinks that maybe life-spans will be drastically extended in the near future. George Dyson is afraid we will discover everything about Molecular Biology without understanding the origins of life.
The idea that fascinates me most is from Geoffrey Miller, an evolutionary psychologist. He tries to answer the question: Why don’t we find extreterrestial cultures? If they exist, have evolving cultures a tendency to eradicate themselves? He has a radical idea: Cultures get lost in computer games one day. As soon as technology is highly evolved, we all play EverQuest. Literally.