I don't agree with you at all.
For one, he's not voting republican anymore. I'd say that's a huge fucking win.
I'm sorry I couldn't make him change overnight, I can't save all of the oppressed people overnight.
Believe me I would love for people to be more understanding and empathetic. Hell, if I could snap my fingers and make the far right vanish I would. But that's all fantasy.
The reality is that people have good and bad in them, most people can evolve if exposed to the right stimuli.
So what it took a long time for this guy to get to where he is? It's not perfect, sure, but is the world objectively better off with someone who doesn't hold shitty toxic view anymore? Absolutely. Better than leaving him to his own devices, and removing any external factor into catalyzing change in his mindset leaving him the same or far worse off. Positive influence is positive influence. Removing the positive influence removes reinforces the chance that you will stray further off course.
So you wasted 15 years of time and effort to change a single person's mind.
Thing of all the useful things you could have been doing politically instead of that and you will realize how empty, weak and vapid your argument is.