frogs - because if you believe something strongly and you know you're right, then it's dishonest to smile politely when someone talks what you believe to be bollocks.
I remember being taught by nuns that if I were ever to come across a benighted atheist (such as my now self), then it was my duty to lead them to christ. Not doing so was a selfish self-indulgence, allowing someone to go to hell in the name of good manners.
I can see their point of view. Mad, not very good dinner party guests, but logical, surely?
Also, I'm sure Dawkins or Aloha don't rant on at dinner parties or whatever, berating religious believers (although perhaps some of us will find out next week - perhaps she does!) but if you're participating in a discussion, of course you're going to say exactly what you think, perhaps in a blunter manner than you would in a social context because in a social context it wouldn't be good-mannered.
Come to think of it, I don't think I ever did attempt to lead anyone to Christ. Selfish, me.