“… unintentionally kill someone.”
If you are in a situation that you use brass knuckles, you had better be sure the use of the weapon is justified. Just like with any weapon.
Someone taps you on the shoulder, you turn around and decapitate them, then find out they were a Girl Scout trying to sell you cookies, you are going to jail. You pull brass knuckles in a brawl and someone gets injured or killed, you could face charges or lawsuits. The use of the weapon has to be justified by circumstances.
But yes, the intent of brass knuckles is to increase your ability at the expense of your opponent, including death as a possible outcome for said opponent.
I’ve never held brass knuckles, but my limited experience holding things suggests gripping with your fingers through loops could make your fingers sore. Ever had a ring crunched between your fingers because you shook hands with a brute?
But used properly (and sized properly, I assume), the brass edge takes the blow and transfers it to the long bones of your arm through the palm of your hand, bypassing the knuckles and hand bones.