Why do Christians proselytize?

Seriously, what's the point? I mean, clearly you are so sure of your beliefs that nothing anyone says will change them, so why do you think other people will change based on what you say? Wouldn't it just be better to leave people alone to believe what they want? I mean, yeah sometimes it can be amusing, but most of the time it's just annoying.

And before I get a bunch of answers screaming how I'll "convert if I only knew about god!" let me just say now that most Atheists--myself included--have reached our position after thoroughly questioning Christianity and other religions, and know just as much, if not more, about religion than believers do.