I agree that you can't own an art style in the US and I don't know if there's any other legal basis for artist's claims.
Legality doesn't automatically deal with problems that are not based on whether something is legal or not. Losing money is losing money, regardless of if its the result of something legal. And people can feel devalued by something that is legal. It just means that the government will not use force to intervene in what you're doing and may in-fact use force to support you.
Picasso is dead, so he has no ability to feel devalued. Artists who are alive do have that ability and other living people who value his works do as well.
I myself support and love this technology. But it is clear that it causes problems for some people. I would prefer for it to exist in a form where artists could get value from and be happy with it too, but that is just not the case at present.