It's not silly at all, and here's why:

There is certain behavior (constant personal attacks, racism, etc.) that will get an account banned. Sure, that person can set up another account, but if he or she engages in the same behavior again, that account will also be banned. The banning policy discourages certain behavior, point-blank. If someone really has the time and inclination to try and circumvent this over and over, so be it. There are, thankfully, precious few people around here who are that level of pathetic.

I see it here and I see it on every other message board I'm on. People who get banned keep coming back. You don't need to be a wizz kid in order to get back on the site after being banned. It takes 2 minutes to sign up for a new account.