Using neural nets trained on other people’s work to create (and often profit from) new work in their style without compensation is problematic. I don’t think that doing the same for upscaling algorithms is.
Upscalers can reduce the hardware requirements for games, support remastering old media, etc. which isn’t really the same as laundering someone else’s creativity and profiting from it at their expense. Upscalers feel more like bicycles for the mind than crude replacements for them.
I haven’t thought through this fully, and I’m open to being proven wrong.