Hard Rock has a bad rep and is often associated with drinking, drugs, Satanism and teenage rebellion. Yes, those are some components of hard rock, but that's not what hard rock "is."
Hard Rock is a music genre, not a set of anti-commandments that tells kids to stay up late getting stoned and drink until that can no longer function. Some people hear those songs and turn them into actions and ways of life, but others (like me) listen to those songs because A) they sound cool or B) the band has other inspirational songs that have more meaning than teenage angst.
Influence is all in how someone handles things. Sometimes people can handle the music and sometimes they can't.
It's all personal.
Rock music is (depending what sort we're talking about at least) probably one of the most interesting and thought-provoking genres out there. A lot of rock bands talk about politics and (realistic) sex and angst and being part of the unglamorous working class, things that teens can relate to and want to know more about. To be honest, what's the alternative? Pop music where children are brainwashed and taught that if you're not pretty and rich, no one will care? Nonetheless, just let kids listen what they want to.