"It is therefore that I say: certainly do come up with all kinds of hypotheses, but if they haven't been tested, be careful not to believe in them too much."

This is good advice. I'm one of those who throws around EP-style explanations pretty casually. But I think there's an unrecognized use of this kind of casually rationalistic thinking: it exercises our minds to come up with a materialistic reason for all sorts of social observations. Even if we can't test our EP conjecture for why people support the underdog, just formulating and considering it inoculates us against thoughts like "It's just moral to like the underdog" or "Things're more interesting that way", or "That's just the way things are" (or even more obnoxious explanations like religious ones).