This is more of a social status thing. Being contradicted and quickly agreeing with the person who contradicted you leads to a loss of social status that people try to avoid. A good way to dodge this barrier is to mention that it's a common misconception, talk about how wide-spread it is, and why it isn't true (evolution isn't THAT incompetent), then ask where they heard it. That lets them take the assertion back without much loss of status.