Couple hundred guys like that in a decent sized city, I’d imagine. Say, they come down with some “new” fatal sexually transmitted virus or incurable sexually transmitted MRSA. 200 guys, 50 women per year apiece, who go home to their husbands and deign to have sex in order to get something, then half of those husbands cheat on their wives. Do the math. Epidemic in very short order.
Depending on the speed to death and the % of transmission, something like that could get very scary indeed (especially if condoms didn’t work).