Well, Russia recently passed a law making the four most common anatomical swear words illegal. Bitch (suka) is still legal for the moment, but “whore” will get you fined.*
In the case of the US, though, I think it may be polarisation. The country with the biggest pornography industry and the biggest obsession with “free speech” may have the largest number of adults reacting to it.
I used to stay fairly frequently in an hotel in Bavaria, and on several occasions I took non-German-speaking British engineers with me. I had to tell them that the “pornographic” magazines on the hotel bookshelf were just ordinary German magazines, because front page nudity wasn’t anything out of the ordinary (this was the 1990s, things may have changed.) Had I taken some of the people from our operations in Kentucky or N Carolina, I think their Baptist heads would have exploded.
*Edit - Umberto Eco says that to understand what a culture spends a lot of time doing you need to see what is forbidden by law. The application in the case of swearing in Russia is obvious. As a student, I remember someone who, having spent a year working in factories in both the US and the USSR, was able to say that the Soviet and US blue collar classes had evolved more or less the same swearing phrases by convergent evolution.
