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Started on the internet in '89.
... and it wasn't that rude. There were flamewars, sure, and some of them were legendarily Epic... but they weren't the norm.
Now, everyone assumes that being dickish is normal behavior for the internet.
Population alone makes a big difference I think. The old internet required a higher knowledge level kept activities more segregated and had a lower population density. Less people from a higher shared knowledge level doing separate things. Flamewars happened but you usually knew where and with what topics. Less people also meant knowing other users much better.
Now, we have everyone who can find the letters on a keyboard or poke a mobile device screen. Every .php file ends with a plee for conflicting visitor opinions. Topics bleed over between forums let alone discussion threads.
We've gone from Farmvill Idaho too the Akihabara in Yokyo; of course there is more lights, noise and people.