Should medical operations, decided by the parent(s)/legal guardian(s), be performed on minors if the minor does not consent to the operation?
Depends on what the surgery is for
I think it depends on the surgery and the parents ethically but legally parents can do many things.
Absolutely. That's pretty much what being a minor means: your parents make the decisions for you until you're old enough to do it yourself.
Yes. That's what they're supposed to decide. It sucks if the dice were rolled and you are screwed though. You can always apply for emancipation.