Anger and Bitterness on the Internet

This is not exactly an original subject by any means, but something that I've just noticed more and more lately.  Why does it seem that people act like such children on internet forums?  I formerly thought that it was only certain forums that people decided to throw tantrums and deride and debase other people on, but the more I peruse the internet, the more I see the same type of behavior.

Even on various Disney World fan forums I've spent time on, people are incredibly bitter and treat anyone with a mildly differing opinion than them like a complete moron.  Why do we feel so entitled to having the only valid opinion on the internet?  Even if we don't like someone else's opinion, why do we feel the need to insult their intellect and taste because they like a certain theme park attraction over another?  Now, I'm not coming here to complain because someone was insulting me, because when I see conversations like this I tend to steer completely clear of the silliness.

Anyone else have any experiences like this, where things just get ridiculously out of hand? I'm starting to feel like the anger associated with politics is starting to bleed into even the enjoyable, allegedly relaxing parts of life!  Can't we all just get along?