When it comes to the big issues of the day it is tempting to try to silence those who disagree with you and who complicate a question that you wanted to see as obvious and simple. And the easiest way to silence someone is to portray him as some kind of lunatic or extremist, a person outside the consensus of ‘reasonable’ opinion, and beyond the pale of rational argument. But the true extremist is the one who argues in that way, and who cannot entertain an opinion without wanting to protect it at all costs from those who disagree with it
http://www.eppc.org/publications/new-politics-climate-change-space-deniers/