I find it difficult to understand the immaturity of not being able to separate the art and artist. It’s really not difficult. I think some of it is performative for signaling to one’s peers that they are on the “right side” of some issue or imagined virtue.
It's not about immature people being unable to separate art from artist because it's difficult. The issue is whether it's the right thing to do.
I feel pretty confident that I could describe to you a case (either real or hypothetical) where you would reject an artist based on their personal behavior, rather than their art. You would find it quite difficult in such a case to separate the two.
So the question is where to draw the line, and everyone answers that question differently.