You focused on unwillingness to change one's opinion. That's certainly a definition, but the more common one in use is about prejudice, especially prejudice based on inherent traits like sex or race or sexuality. I'm sure you're aware of that, which is why it's confusing that you're acting as if you're not.

I don't dispute that it's extraordinarily difficult to get people to change political opinions, especially on the fringes. That was never my contention, I made that pretty clear with the example of bigoted communities I chose being white supremacists. Not sure how you could misread that, unless you wanted to.