On one hand, I think it might be ridiculous for an artist to get to "own" a "style" of art. In the first example on this page, none of the art looks plagiarized. It looks like what every artist has done: been inspired by or borrowed ideas from other sources.
But on the other hand, if left unchecked, this will further harm our creative industries. We're going to be starving out our artists because robots can generate art _far_ more easily than they can. If this continues, it disincentivizes anyone from trying the already very uphill battle of making a living by creating art. One might say, "capitalism, baby! we don't need those artists, because we have AI and look at what it can do in seconds!" But I think that even if AI can "discover" new art styles and trends, there's something lost by humans not doing it.
I don't think AI will be able to replace human creativity for discovering new paradigms as fast as it will replace human application of existing paradigms. And by doing the latter really well with AI, we're killing our ability to do the former. We'll end up with a sterile art trajectory.
I guess my uncertainty is: something about this _feels wrong_ and yet I cannot point to any one moral/ethical thing that feels wrong about it.