'In his celebrated book, 'On Liberty', the English philosopher John Stuart Mill argued that silencing an opinion is "a peculiar evil." If the opinion is right, we are robbed of the "opportunity of exchanging error for truth"; and if it's wrong, we are deprived of a deeper understanding of the truth in its "collision with error." If we know only our own side of the argument, we hardly know even that: it becomes stale, soon learned by rote, untested, a pallid and lifeless truth.'
Carl SaganWhen you look more generally at life on Earth, you find that it is all the same kind of life. There are not many different kinds; there's only one kind. It uses about fifty fundamental biological building blocks, organic molecules.
Carl Sagan