Nicki. She talks only about s** and nothing else! I mean yeah the others might not be too good, but she sings songs that show young girls that they need to be bitchy and horrible to get attention, and that showing of every little bit of your skin is great. blerk.
Hmm... I would say that Kesha is definitely the worse artist out of all of those, but I don't know anyone who actually looks up to Kesha or tries to follow her, so even though she's a complete moron I'd have to say that she hasn't done any damage to youth culture.
Katy Perry hasn't done anything bad that I know of. She seems to just be a regular girl. Yes, she talks about drinking and partying, but she just sings about things that regular college girls do anyway. She hasn't had an effect on youth culture at all.
Lady Gaga has done a lot for the gay community. I personally don't think that's a bad thing. She's had the strongest effect on youth culture out of any of the artists that you mentioned, but like I said I don't think that encouraging homosexuals to have the same rights as heterosexuals do is a bad thing.
Marylin Manson - wtf? Does he even count? He hasn't come out with anything since 2000. The only song most younger kids know from him is "Sweet Dreams" and they just think he's a weirdo. He has no effect on youth of today.
Nicki Minaj - I think that I'd have to say that she's the worst of all of these. The other people either had no effect on youth culture or (in my opinion of course) benefited it, but Miss Nicki is definitely a negative influence. There are (sorrowfully) lots of people who try to copy her "baddest b****" attitude and style. She hasn't done much for society besides convincing ugly girls that they look like Barbie so, in my opinion, she is the worst.
I wouldn't say I'm a big fan of any of those, but I don't think they've really done anything to damage youth culture.
The worst (by far) would have to be Beyonce, who constantly sends out the message that it's okay to rip off other people's melodies, lyrics, choreography, costumes, etc - and that if you shake your ass while doing it, you can be a big star. And as we've just learned, you don't even need talent - you can simply mime to a prerecorded track instead.