I think I am essentially utilitarian about this. I don't think it is, in general, worth an individual's resources (time, effort, chance of being harmed) to try and rehabilitate a random adherent to hateful ideologies. People less beholden to evil are more attractive targets, and a bullet to a fascist head is a lot quicker.

Likewise though, I don't think it is worth a society's resources to mass execute a large subsection of their population, and so rehabilitation schemes are preferable.

To be honest though, I think most people only fall to fascist beliefs because of the appearance of an open community and the sublimation of their feelings of failure into hatred for some other group. If we ever succeed at crafting a more pro-social society where all have a place and there is a real sense of community, I think the majority of the current fash sympathizers would deradicalize themselves.

Also, on a personal note, I too lost a friend to fascism. He had reactionary views when I first met him, but also seemed to be a deep thinker that wanted a better world. Over time, I thought I had softened many of those views, and had even gotten him to accept the necessity of a universal, not-for-profit healthcare system. However, I could never find the ground to get him to deal with the (honestly pathetic) trauma of having been (supposedly) cheated on by his high school girl friend.

Dude just kept dating girls currently in, or fresh out of, high school. The relationships obviously never worked. Then he started dating a church girl (who was 17 while he was ~30) and they got married when she was like 19. He started telling me of the new found importance of god in his life, how our world was removed (this was before trump so that word held much less YIKES), how porn kept us lonely, the need for nuclear families, etc. I pushed back lightly, but he seemed happy for really the first time.

Then, predictably, they got a divorce as you don't marry a child and think it'll work out. His response: go full hate women MGTOW and fast track the alt-right pipeline to fascism. The last time we talked he was telling me about how helpful he'd found this new guy, Jordan Peterson. I cut ties after he said America's downfall began with women getting the right to vote.

I once considered him like a brother. I now sometimes have nightmares about him killing me or his ex-wife.

Edit: Oh, I had a friend that dated him for a while. She confided in me when we reconnected years later that he had stalked her for years and she had gotten a restraining order and a gun because she was so scared of him. I'd already cut contact at this point, but I also never saw this side of him. We were definitely at our closest while he was also stalking her.