If we made laws that protected the uniqueness of first names to artificially boost the name creating industry, stealing names would become a crime as well. Name theft in the sense of the law would be theft but it wouldn't be like stealing a car, because stealing a car would have negative repercussions even if it were legal.
Enforcing everyone has unique names might have a high enforcement cost, which is why it may not be worth cost to society. Likewise enforcing copyright for consumer use has become harder and harder as well and at some point it won't be worth it either. Enforcing property laws however is cheap because it's hard for everyone to mass-steal cars and protect their own property.
