For starters, I have a perfectly good vagina for you to use... second, as the previous poster said, do you like having things stuck up YOUR ass? Obviously a lot of guys do, but even in that case there are different things going on (like the prostate)... a lot of guys aren't very good at sticking their dicks in the hole they're supposed to stick it in, and it's bad enough to deal with them sticking it too far, too hard, too fast and poking the wrong parts. Letting a random guy loose on an even more sensitive part which is really meant for things going out not in...
All that said, I do have anal, but not with just anyone. And I do it because my partners want it. That's not to say I don't enjoy it--sometimes I really do. I really get off on things that make my partners go crazy--it's why I do facials, etc.--it's fun to give them what they want, to act like a girl in a porn, etc. but it's not a sex organ and it takes work to make it fun for a girl, and even when fun it can be uncomfortable and painful. So, I do it, and if done right, I'd even recommend, but it's not an automatic thing.