Why do so many people have an issue with separating art from the artist?

As someone who grew up as a bit of a bookworm I've read plenty of great authors who are or were anything from flawed individuals to morally abhorrent proto-fascists, I've always personally adhered to the value of separating personal beliefs about the moral worth of someone's character from their merits as an artist. There are plenty of terrible artists who are the nicest people and vice versa and I would rather have amazing art made by terrible people than something mediocre made by someone I like. To be clear this isn't a defence of any crimes talented artists commit, they shouldn't be above the law. I just find it hard to understand why such a reveal would taint the work they have produced.

Why do so many people have an issue with separating art from the artist?
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