It's not a small number, and like you point out, this is human nature, so asking people to stop is pointless. If people always acted rationally and with empathy for others, everything would be much easier. There would have been no Covid pandemic, no global warming, no drunk driving, and so on.

Yet here we are, needing laws, cops, vaccines, and so on. Asking people to only have absolutely safe sex due to its external effects is about as useful as asking them to stop eating meat due to its external effects.