I've never been banned for a stupid reason (I was only banned once about 8 years ago, and I was being an immature kid at the time, very legitimate reason).
I have banned several people though, most of them for them doing something stupid. I used to be an admin on a CSS:Source zombie mod server. You can find a lot of people doing stupid things there. One guy was standing around doing absolutely nothing, then raged when he got hit by a zombie. He came back (after I gave him a warning, and a kick), and raged even more when he was randomly chosen to be the starting zombie. He refused to do anything, because he felt he didn't deserve to be a zombie. Banhammers aren't picky, neither should he (I told him that in his last seconds on the server). I banned a lot of people for excessive immature behavior (mic spamming, tossing tons of rude insults around, etc.), but I don't think I've ever had any problems with a hacker. The few claims I did get were because someone didn't like someone else killing them, so they tried to get a ban going.