Ok, I guess I'll take the opposing side.
Internet cannot cause depression.
Thats like saying reading can cause depression. Or TV, or food, or anything else that can be done in excessive amounts. Ever get depressed when you bike for 35+ hours a week? Or get a suicidal urge from your daily exercise routine?
Internet is an outlet. Personally, I think its a way better outlet than say television. At least on the net you can basically arive to one thing, meaning you can look at JUST something happy. Where as on the TV, you're along for the ride. Could go from Simpsons (Funny), to CSI (Murder, death, lying, all that 'good stuff'), to the news (Murder, genocide, corroption, politics = evil, cheating). So the net is better in that aspect.
And I also believe that the net would be the anti-thesis of "causing depression". Rather than sitting in your room, doing nothing, THINKING about suicide, you can get online, play games, talk to people, read, and a million other things. Now, someone said isolation cause depression somewhere up above. I buy that. BUT, how can you be isolated on the internet? It spans, what, only the world? You can find EVERYTHING on the internet. I think you're rather unisolated. As far as interaction is considered, you have a million messengers, web cams, voice chats, message boards, e-mails, blah blah blah. You're connected to people.
Hope I did that side of the argument some justice.
SALLY! COME VISIT ME AND BLUE!!! We'll give ya some flesh with flesh time
