Because there are rules Duh and the mods do a great job(except maybe for twes :P)

You must be new to the internet if you think the rules here are harsh.

This is a general audiences website. Sites like the Steam forums or IGN will ban your ass long before say your first swear word...there are tons of forums that are way more strict than this one.

This line of reasoning is known as a technique of neutralization.  Or in other words an attempt to rationalize bad behavior.  If you've ever heard the phrase "Two wrongs don't make a right." then you should understand why this doesn't work.

If we say its ok to insult people because they say something "stupid" the entire thing becomes subjective and suddenly mods are forced to make determinations about whether you were justified in insulting someone.  The far easier way to handle it is to disallow insults altogether (a far more objective test) and have people report any post they think violates the forum rules rather than attempting to "deal with it" themselves.  But more importantly we just don't want the kind of atmosphere where you could be insulted for saying something.