Is fixed bad for your knees if you dont skid / ride high gear?

"incorrect use of a bike" would cover what Hippy calls the "too much/too soon" syndrome- as in: yep you could do standing starts in a 100 inch gear, but best if you spend 3 month creeping up on it from a 50 inch gear.

Yep, I purposely used that phrase as a "catch all" ;)