I think it is completely fine to want to remove material you don't want to see. I'm in favor of it in games, I won't create a double standard for other media.

There is, however, a larger discussion, I think, about how people experience media that is problematic, and our tendency to want to sweep the problematics of it under the rug. The slurs are bad, but removing them doesn't change the overall ableism in Homestuck. Also, as it was pointed out by others, the execution is... Not the best. It proposes to remove slurs, but then also removes other stuff that are, categorically, not that. I understand the intention behind it, but eh. Could be better.