One of the main excuses for kids deterioration in behaviour is TV shows/video games. It mainly seems to be the media who mention this which is pretty ironic.
I don't think TV or games can really blamed though. Afterall, violent TV shows have always been around (in fact there's probably not as much around now as there used to be) and while such games haven't been around for too long really, they're simply expansions from the TV shows and, in my opinion, can't be held any more responsible.
In terms of what's actually to blame for unruly kids, it's most likely a multitude of things.
As I'm 20, when I was growing up it was generally different to how it is now. Me and my brother were raised single-handedly by our dad for the majority of our childhood. He was always out working so he hardly ever saw us. We still turned out well and respectful so I don't believe it when people say things like "not being close with parents will caught behaviour/attitude changes". That didn't happen to us because our dad was old skool and therefore didn't let us get away with things. We'd soon get a slap if we did anything wrong.
In comparison, my sister is 14 and is a right annoying b**** most of the time. My mum doesn't work so they get to spend time together but not too much time otherwise it'll cause more arguments. My sister gets away with anything (unless I shout at her about it) and gets whatever she wants because my mum spoils her big time. My mum knows she spoils her but just keeps saying that it's too late to change and refuses to even try.
While out shopping at one point, my sister was mouthing off so my mum went to slap her. My sisters exact words were "You can't smack me because you're not allowed".
I'm not saying that kids should be smacked just for the fun of it but they should definitely be allowed to be physically punished if they deserve it. As smacking if frowned upon by people these days (in the UK anyway, not sure about other countries) kids think that they're untouchable and therefore think they can get away with anything. That only really applies to the above examples though.
As a result of the different upbringings, I'm totally respectful whilst with company (be that personal or public) whereas my sister has a rotten attitude and seems to think it's acceptable to do as she pleases and treat people like crap.
Our grandparents said the same thing about our parents generation. Our parents said the same thing about us, and we'll say the same thing about our children. It's a vicious cycle. I think this is really situational, like the scenario BIS mentioned with absentee parents. Kids will act out for attention. But I would stop very well short of an all-encompassing judgment that all kids these days are evil little maniacs, and that we should weep for the future. Like it or not, they'll be leaders in society one day.
Okay, time for my input. If I'm being honest, I'm more or less part of the current generation of kids (gasp! the horror!) and, while I am FAR from perfect, I wouldn't go so far as to describe myself as a monster or anything like that. I mean, I don't swear, play violent things, listen to obscene music (actually, atm I've got some Mozart going), etc., and even when I read about or see violence I don't act like the people I see, but I have my flaws, such as a tendency to procrastinate. I've got plenty of friends who are good, honest teens, and we aren't the monsters you describe here. I also frequently help my mother in her classroom, and most of the kids there, while squirmy and pretty noisy, are actually well-behaved.
One important thing I remember hearing/reading that might be relevant is that everyone is the hero of their own story. Your memory typically works so that you are in the right, and your brain is more likely to hold onto happy memories (such as you being good) than others (such as you being bad).
Also worth noting is that, yes, it is parenting, too. There're lots of types of parenting, from incredibly strict parents that only let their kids read/watch/play things for their age groups to really lenient ones that just don't care, or don't oppose their children much. The latter category isn't necessarily bad, though. I have a great buddy whose parents are pretty lenient with him, but they almost never fight, and he describes himself as having a good relationship with his parents.
(Sorry if this is a bit rambly/jumbled, that's just how my mind works.)