Artist's rights and profit

I have some good understanding of copyright law, but as I watched this film I kept wondering about our laws and rights when it comes to art. So since folks who end up at this board will likely have seen this film I have a few questions:

1) If you buy an artist's original work (let's say a painting), you retain it for a while, then you sell it for more than you paid for it, are you unfairly profiting on that artist's creativity?

2) If you buy an artist's original work (again, let's say a painting), then you modify it to make it more or less interesting, are you unfairly profiting on that artist's creativity?

3) If you buy an artist's original work (one more time, let's say a painting), then you burn it in a fire for the heck of it, have you violated that artist's creativity?

I ask because I was surprised at the incredulous responses from the directors and writers in this documentary. They have been compensated for their work, so what right do they have to go on controlling it? I know the violation of law here was mechanical rights, but the directors weren't arguing over mechanical rights, they were arguing over artistic control. I found this quite interesting....