I don't think it has anything to do with politics, religion, or morality. I think it has to do with shifts in society in several ways. A few ideas:
1) Kids are are more spoiled now. They expect more privacy, and whine if they don't get it.
2) Homosexuality isn't as taboo. Guys are more aware that other guys might be sexually attracted to them. Being naked around a bunch of strangers probably heightens this feeling and raises paranoia. I personally don't care if a gay guy checks out my naked body. He can look, he just cant touch. But a lot of younger guys get more freaked out because they're insecure.
3) Young guys don't have as many strong male role models any more. A lot of guys my age and younger grew up or are growing up in a single mom household. I don't want to make any extreme stereotypes; but generally speaking, moms are going to teach their sons to be more private and reserved than their dads would. In my early teens, I had a friend who was being raised by his single mom. One time we were at the mall and went to the bathroom. There was a long line of urinals, and most of them were empty. So I stepped up to one, whipped my cock out and started to piss. While I was pissing, I realized my friend had gone in a stall and locked the door. I thought maybe he had to take a shit...but nope, he was finished in less than a minute. As we were leaving the bathroom, I asked why he didn't just use one of the urinals by me. He said his mom told him it was wrong to let anyone else see his penis because they might try to do something bad to him. We weren't friends for very long (not because of that...just starting getting different interests), but now that I'm thinking back on it, I'm sure there were other examples of him being a sissy. That's just the one I remember most clearly because it seemed so stupid to me at the time. Anyway, I think the lack of dads for a lot of boys these days is probably one of the biggest reasons behind younger guys having absurd notions of modesty.