Hello, avid anti-seatbelt law person here. Also avid mask-wearer. Sometimes there are reasons for things and calling people names without understanding their side is counter productive.
In my case, and in the case of anyone I've spoken with about the law, we don't believe that seat belts are bad or that you shouldn't wear one. We just are opposed to any law that "protects someone from themselves." A mask protects everyone. A seatbelt only protects the person wearing it, and there's no limit on speed or distance. You could be moving your truck from one parking spot to another at 5 miles an hour without a seatbelt, perfectly safe, and if a cop sees you, you get to pay their fundraiser. It's an abuse of power.