This is a very interesting question and I've been trying to think about it properly. Is there one thing that would remove our ideas of empire and colonialism? Something that would lessen our consumption and use of fossil fuels? One religious text that could be taken away that would have led to fewer wars and persecution? But I don't think it's possible. All these things stem from our qualities as humans and art merely reflects that. Remove one religious text for example, and another would take its place. Remove one justification for war and slavery, and another would be found.
And all the awful art in the world, while awful, is reasonably benign. OK I hate a lot of it, but that's just aesthetics.
So I'm going to remove something good. Something I love. Just because it would be interesting. I love music, and I love new and experimental music and music technology. So I'm going to remove the electric guitar. Not that I don't love guitar music, but more because its influence has been so great over c20 recorded music that I'd just be really interested to see what would have happened without it. We wouldn't have had the same blues and rock & roll influences. How would synths have emerged? Would there be another dominant instrument? I think new music might be really different and interesting.