Who says it would be to society's detriment? And a lot of the "art," it could be argued, is nothing of the sort, in particular much modern architecture and "abstract" art (that could be a whole different thread unto itself, in particular about the shenanigans of the architectural profession). More automation of these things will open the ability to create more things up to more people. And it will not eliminate human creation of such for those that want it.
There's also the issue of freedom. If I come up with an idea for a TV show and have the storyline thought out, but could use software to generate a decent script, why should I be forced to hire a scriptwriter?
Union members aren't rich, but they can be extremely lazy and entitled, depending on the union. Remember unions are part of what almost drove Britain's economy over a cliff back in the late 1970s.