Some people put too much faith in reason.
When I read his manifesto it felt to me like it was logically airtight. If you agree with his premises, I think it's difficult to reject his conclusions using reason.
But of course we have much more than reason to rely on when making decisions, and it's easy to reject his conclusions if you use your whole mind, some might say your heart.
I think it's tragic that people, both individually and at the social level, are so good at reasoning ourselves into situations that we just can't live with.