Because some people by nature are competitive. Why does PvP exist? ePeen. I personally don't care about competition, that's not what I want in my life. That's why while I say "lolPvP", I never say ONE WORD against anything related to PvP. Because it's not my playstyle, and as long as it doesn't mess with my beloved PvE, I won't say JACK about it.
If people want badges or accolades or titles or capes or auras or l337 l007 for their "toons" that's "exclusive" because they earned them? Go nuts, I say, make it an option, as long as they don't take anything away that I already have access to, I see no issue with putting some new stuff behind some sort of velvet rope.