Is a shemale a woman with a cock? A woman that use to be a guy but had the cock removed and now has a glory hole? A guy just dressed up like a woman?
If it's a really hot chick that had all the surgery and you can't even tell it was a guy I'd do it and if I found out after the fact it was a guy I'd just be in denial.
A shemale is someone who was born male who alters their anatomy enough to pass for a woman, but does not remove their genitalia. That's the way it seems to be being used here.
There seems to be an ongoing argument somewhere here. I certainly think that it's a bisexual tendency for a guy to derive sexual desire/pleasure from a person with a penis. It seems entirely obvious to me that if you were to look at it clinically, the transgender person still maintains the key components which define masculinity. With regards to psychology, clearly a shemale with the choice to change also feels like they'd rather hold onto some part of their anatomy which we all associate with maleness.
Anyway, if you're willing to admit you fancy shemales (extremely taboo), then why would admitting you have bisexual tendencies (less taboo) be a problem?
I think the key point is sexual desire/pleasure btw -- it's entirely possible for me to see why Brad Pitt (or Hollywood hunk of your choice) is considered physically attractive. I can envy the guy's looks, wish I had the same physique he used to have, the female attention he gets, etc... but I'd never want to do anything remotely sexual with him.
If that didn't make it clear enough... no, I like born females. I like all the things the vagina can do too much to consider a cock, and I like women who aren't at all like men. Nowadays, it seems way too many people forget just how wonderful a pussy really is.
[I don't mean shemale fans here, even men who are only interested in born-female women seem so obsessed with other kinks (like anal) seem almost bored about the part of the body that defines femininity. For me personally, that's just crazy.]