I've never felt emasculated by it, but I suppose it's all in the mindset of how you go into it. I personally don't see butt play to a guy any different than a blowjob. It's a sensitive area that feels fantastic when stimulated. I think keeping that logic in mind can ease some of the misgivings you or your partner have about the entire idea.
Anal play is all about enjoying the sensations and enhanced orgasms for me. I've never done pegging with a partner; however, I did have an ex that wanted to. I think even there it's more about trust and enjoying the experience than "being a man". I think worrying about being masculine only leads to missing out on amazing experiences and potentially a deeper connection with your partner.
What?! No. I've also never been pegged either, but I'm holding out hope for that day to come. Anal play is another way to experience pleasure with your choice of partner or partners. There should be no shame ass ociated (get it...moving on) with it on either end.