As I said in another thread, 4/20 started because a group of kids at some school started getting together after school, at 4:20, to smoke pot. That's it. Nothing big and fancy. Just a trend that caught on well.
http://en.wikipedia.org/wiki/420_(cannabis_culture)
Check it. And yeah, it's Wikipedia, but why would anyone make up such a boring origin?
So, stop making it like potsmokers who celebrate 4/20 are the bane of our existence. They're just stoners, after all. They aren't going to hurt anyone other than themselves.