>Lord knows that e.g. "evolutionary psychology" (which this would fall under) is packed with just-so stories.

I think this has to be admitted, and that any explanation based on evolutionary psychology should be viewed more skeptically than other arguments. However, I think it's absolutely true that genetics do influence our psychology to some degree. And so, there must be some evolutionary psychology claims which can be said to be true. At a very high, and very basic level, some are so self-evident that no one bothers to make them: ie, that sexual attraction exists, is a strong motivator for most people, and must have a basis in evolutionary fitness. Obviously things can get more murky when you want to discuss behaviors with more nuance or complexity. Further, even when a claim is probably true it's quite hard to actually test in a scientific manner. You can isolate the behavior, but not the explanation. How can you truly prove that a behavior is caused by evolution rather than social pressure?

That said, I don't think the whole field can be thrown out, despite your accurate claim that the field can be a bit of a mess.