Even if the rules dis-allow generator use, that is the extent of the offense. The person running the generator may be evicted from the campground but that's about it.
Vandalizing someone's generator is against the law in every state as far as I know. Doing so can get you arrested, fined, even jailed if the law catches up with you. If the owner catches up with you first the penalty can be even more painful and/or permanent leading to even more serious criminal activity (assault or even worse).
Camping in a remote location is one way to assure you will not have to endure listening to someone's generator (unless it is your own), camping where there is AC power available is another choice. If you choose to camp when and where generators are allowed by the rules you have made your choice. As much as we would all like for the rest of the world to play by our own rules, it ain't going to happen. Generators are kind of expensive to own, run, and maintain. If you talk the person running a generator you will probably find that there is a good reason for it to be running. If the campground allows generators and you cannot get them to change that rule for you, changing campgrounds would probably make you, the generator owner and the campground host all happier campers. I have been annoyed by generators in campgrounds, I have run my generator in campgrounds, and I have been the campground host, in my experience the most unreasonable people fit in the first category (the annoyed).
Why not just get out there and enjoy the camping? That generator will run out of fuel eventually, long before it has run as long as you feel like it has been running.
