I don't even feel this way, because we've seen it work just fine with Spidey and Superman. But a guy would need the right build. The problem in nearly every case that I know if is that guys go part-way (see: Avengers Cap, X-Men) instead of just going balls out, and so it ends up taking the worst from fantasy and reality. USO Cap was done as a joke and he acted like a joke, and so it didn't come off well, either. I also know lots of comic movie fans make a stink over it, but why do Spidey and Superman get passes? It's just a lack of willingness by studio decision-makers to just go for it.