...But it's okay if straight guys get reamed in the ass by shemales and strap-ons?
Please don't tell us what's okay and what's not just because it doesn't resonate to your particular taste in porn. Some people dig it, some people won't. Don't like it? Move on. Simple as that.
Besides, it's your own semen. If that's gay, then giving yourself a handjob whenever you watch porn should be enough to brand yourself a homosexual, if that's what you fear.