Even my mountain biking gloves have fairly decent knuckle protectors, the old ones i had probably saved my fingers a few times with various falls/hitting things.
They have a genuine use and are normally rounded as to not cause unnecessary harm to whatever your hitting.
But maybe if you went in to a pub and started kicking off while wearing them the police would have something to say about it! It's the same as a screwdriver and hammer, fine to have in your car but if you keep it in your drivers door pocket and you're clearly not a tradesman you can be done for going equipped, it's all about context.