Well, "perfection" may not be the correct word - blame it on my rusty English
But here's what I mean - even though Rand suggests that morality be within reason and all that, and that reason, truth and self-interest should be the main focus of a man's life, there are going to be people who don't follow these rules, and take it the wrong way.
This endangers the ones who do, because this kind of a society seems to be in a very delicate balance - it relies on reason to keep everything in order.