It's an interesting question. Judging by Eliezer Yudkowsky's story in Is That Your True Rejection?, they would be likely to say something that sounded good even if it's not their real reason.

Hi, I'm new to this blog. I haven't read all the essays and whatnot, so if you read something I say that you think is bull, I'd like it if you linked me to the essay.

Anyway... Regarding the dragon and the garage scenario: what would the dude say if I were to ask "how do you know the Dragon is there if it's impossible to know if he's there?"