I don't think the matter lies in judging... I can go to someone's show and judge that it is AWESOME! I think the problem is when you enter ready to find fault. When you can't admit that that piece was cute. Or despite some obvious technical errors, that that class has a lot of showmanship. Or that school is JUST recreational/competitive/professional, so no good can come from it. Ect. If you go into anything only looking for the faults, than that's what you'll find.

I think it's fine to "judge" things mentally (good, bad, or something in between). We can learn from others' mistakes and successes. However, I've always found it best to listen to my mom... if you don't have anything nice to say, then don't say anything at all! There's no need to tell my students what's wrong with other schools or say anything negative to anyone (even if it's true). It will only come back to bite you.