Are you, personally, harmed by someone watching porn?
Maybe it makes society as a whole weaker compared to other societies but that doesn't mean your society actually loses anything. Countries have nuclear weapons and multi-national defense pacts now. Just because China has several times the population of the US and could win a conventional war, doesn't mean it's gonna invade.
We don't live in tribes of a few hundred people who are constantly on the brink of starvation and/or genocide anymore. But many people are still governed by instincts from that environment.