When I first started to bottom, a lot of the guys didn't want to wear a condom. Especially at places like an adult bookstore. They promised they would pull-out. And while many of them did, spraying their load all over my butthole, they would also re-enter me. At this point, I rarely (if ever) protested since I was horny and wanted to cum myself. And nothing facilitates that more than having a cock inside you.
As far as STD's go, the real big one is taking HIV+ (aka "pozz", "toxic" or "scum") semen up your gut. Some of the guys seeing I had a tiny cock, asked me if, "Do you still fuck your wife?" When I said "No", they had no reservations giving me their "charged" load. But I hear that this happens a lot to submissive coukold couples... where the wife gets pregged and the cuck get's pozzed.