I think that it is harmful to not allow men to see another men naked. In the gyms I go to they have recently started putting up partitions between showers, changing rooms in the locker rooms, and one even went so far as to wall up the entrance to the sauna so the entrance could be from the pool, which forced everyone to wear a bathing suit. I think that the primary focus on this is usually homophobia. Some people complain very loudly about other men looking at their junk.
What I find disturbing about this is that the few who are very vocal about this effectively impose their opinions upon everyone else. I think that if you can't stand to be naked in a place where nudity is permitted, you probably shouldn't be there.
As to why I think this is harmful, men are no longer secure about there bodies nowadays. Plastic surgery, liposuction, etc. are heavily on the rise among men in America. On top of that, installing dividers, shower stalls, changing rooms, and even partitions between urinals sends a clear continuous message to everyone that being naked or being seen exposed is not okay.
One time I had someone ask me what I would do if another man hit on me. I told him I would say I wasn't interested. The stunned look on his face spoke volumes; it had never occurred to him that this could work. Unfortunately, that seems to be the case for most men nowadays.
I did fib a little to my friend, however, seeing as how I'm bi. But still, picking someone up in the locker room because you like the look of their genitals strikes me as more than a little shallow. It's kinda like walking up to a top heavy girl and saying, "Nice tits. Wanna fuck?"