I'm all for it-- I got into makeup through theatre and my dad actually taught me a lot about it as a former theatre major and college mime, including advice on color and on what theatre tips weren't applicable to everyday things.
I think makeup is for everyone. Whether it's part of a costume/job, there to invisibly highlight a feature or hide a flaw (just the way many women use it), or to be fun and colorful, everyone deserved to have fun with their appearance however they feel good doing it.
Besides, it looks good. From a purely aesthetic standpoint, I love a man in makeup.