A developed society needs a developed culture. Adopting European artists and scientists during early XX century helped US affirming themselves.
This scheme as you so vehemently put it, is really aimed at getting more pretty things on people's walls. To do that, you need cheap and hopefully somewhat unique. Instapainting allows people to have both because they employ non-creative people who paint. I simply can't entertain the idea that the Chinese artists are being exploited by Instapainting by the very notion that they are being paid less than an artist would be in the US.
Give me one argument why they should. You speak like it's an axiom but I don't see any reason to be a protectionist in this matter. Especially when the customer base is as global as it is (I'm a customer and I'm much closer to China than the US).