Those books were genuinely meaningful to a lot of people. And until relatively recently, JK Rowling was a bit of a liberal darling. I remember an interview with her talking about being on welfare and how we should care for the poor. The books were clearly an allegory for fascism. I don't blame anyone for getting that tattoo. My mom read me the first 3 or 4 books as a child. I waited in line at midnight for the release for the 5th. It was deeply meaningful to my childhood. If JK had not outed herself as a piece of complete trash by the time my mom passed away, I likely would have gotten an HP tattoo. I'm very glad I did not.
Anyone who got one after she outed herself is a POS, though. You just generally can't tell when they got it.