I agree with you in the abstract ideal, but for a lot of people, this choice is roughly as good as it gets. In place of moral compasses, most people have thermometers they use to read the room, adopting belief systems and then enforcing them brutally, with no room for anything resembling moral reasoning, nuance, or basic human decency. The majority of the variability tends to be in 1) the belief system they choose to ingest and 2) the degree of passion with which they choose to engage in it. I'm not throwing my hands up and drawing a universal false equivalency here: Not every possible manifestation is as harmful as every other, and I have no trouble saying that the dehumanization and hatred that marks the strain of mainstream idpol leftism that's currently popular[1] is nowhere near as dangerous a manifestation as that of the alt-right. I don't see a lot of moral distance between the _participants_ in either of these ideologies; as far as I can tell, circumstances out of one's control have an outsize influence on which ideology most people end up as footsoldiers in. But the way in which people's barbarism is sublimated is extremely important from a pragmatic point of view, and I'd much rather see Sam become a mirror of the old man described than the modal alt-right participant at that rally.
Taking the author at her word[2] when she describes how Sam started out, it sounds like he may have been in touch with the sensitivity and decency it takes to approach others with basic empathy. But such a state can be fragile and it sounds like Sam's reaction to the incident at his school knocked him out of that orbit. In the best-case scenario, it's a temporary situation, but the author's claim is that Sam is at a point where he's got a lot of confusion and passion and rage that he's sublimated into politics, and perhaps the best we can hope for is that the path of hate that he picks is one of the less harmful ones like garden-variety identitarian center-leftism.
[1] I'm aware that this is probably an extraordinary claim to many here, so here's a simple example of what I mean. FTA:
> I’d never in my life backed the “masculinist” cause or imagined that men needed protecting—yet I couldn’t help but agree with Sam’s analysis.
The idea that the author doesn't realize what an abhorrent view this is is chilling; people and their lives are insanely complicated, and there's no group that's flatly-generalizable enough that a decent person would never have occasion to imagine they may need protecting in some scenario or another. There's no difference, at its fundamental root, between this and other more recognized forms of dehumanizing people by erasing their individual identities.
[2] Though perhaps we can't take this for granted: as evidenced by other parts of the article, she doesn't seem like a particularly decent person herself.