Look, I'm not saying we shouldn't be registering cars I'm just saying a licence plate is intended as a vehicle tracking ID. That's the whole point. I always considered licence plate customization at best tacky. If I want to add some decals and bumper stickers and such, I'm not going to put it on a state issued ID tag.
For the record, I think customized graphics on your credit/debit cards, check designs, etc. is just as morbid. You don't "own" these things, they're not part of your identity, and letting them trick your brain into pretending that they belong to you and are an extension of your "self" by adding fancy designs is kind of gross. They are symbols that reference you, they are not a part of you.