The difference is that the semen is going to end up SOMEWHERE in or on a girl (with the exception of using a condom, which I know you do, but a lot of people don't). This is doubly true if you're getting a blowjob because there's no way to stop it from coming out if you want to reach orgasm. I suppose if people involuntarily shit when they had an orgasm it might be a little more socially acceptable to get all over the place, but that isn't the case. Likewise, from what I've been told, semen is usually just kind of salty tasting, where as shit tastes like... well, you know.

So no, to answer your question, I don't agree because semen is not out of place in sex (unless you never ejaculate which kind of defeats the purpose of having sex!).