Samantha Escobar at Blisstree has the most succinct summation of why this is cool:
We all know that our society often fat shames people they deem overweight and sometimes body shame those declared too thin, but many men and women consider very muscular women to be “gross” or “unappealing.” I find this strange, since — while I don’t remotely condone it — fat and thin shamers tend to at least cite health as a typical reason for being assholes. When it comes to insulting muscular females, this logic makes no sense; typically, those women work out frequently and eat incredibly well in order to achieve the bodies they have… We’re “allowed” to be strong and toned, but give us some solid definition, and bam — suddenly females are not “feminine” enough anymore.
This MAC ad takes body builder Jelena Abbou and treats her with the glamour they would any other model, even as she gives each and everyone of us a ticket to the gunshow. Striking a powerful pose indeed. Also, relevant Kate Beaton comic.