I don’t think this is an easy question to answer without some qualifications.
There’s bodybuilding and then there’s BODYBUILDING.
In some sense, this is not much different than other physical contests…who’s the strongest, who’s the fastest, who can jump the highest, etc. We give prizes for those activities, and for the most part they’re not questioned as immoral.
I think some take bodybuilding as a erotic or sexual titilation sort of thing. While there are undoubtably those who oogle bodybuilders of both sexes, many see it as a sport…no more, no less.
I’ve competed in several (bag)piping contests, and nobody has ever questioned my need to show off my…snuffle, chortle “skill” even though I took home a blue ribbon one year.
Methinks it’s really important to look at motivation when considering the moral implications of bodybuilding. Competitions can be motivation for improvement, regardless of the sport or activity, and if seen as such would seem to be morally acceptable. However, there is a line that must not be crossed, a line that may not be all that clear and that is of vanity.
If a person bodybuilds as a sport, i.e. sees it that way, trains proportionate to their time available (doesn’t take time away from family, etc.), doesn’t use harmful suppliments and anabolic steroids, trains intelligently so as not to do long term damage to their joints, ligaments, and other parts and does not obcess over the way they look, it does not seem to be morally objectionable.
However, would also seem that it would be somewhat difficult, depending on an individual’s circumstances, to meet these admittedly arbitrary criteria (I just pulled them off the top of my head).
Methinks that one can tell a lot about another person’s sense of vanity. I used to spend a lot of time in the gym working out. The more serious bodybuilders would dress modestly, both in the gym and out. Perhaps they KNOW that they’re bigger than everyone else ;), but I think that many of them didn’t have to show off, and used competition as a motivation to keep themselves fit.