Couldn't have said better myself. It's pretty sad to seem the majority here just handwave this. Of course, we won't know if this movie theme is going to be portrayed well enough until release, but to just deny any kind of criticism in this context is just naive.
The problem I have with this is that it essentially says that decrying an ideology requires no acknowledgment of legitimate material conditions that might explain it. It has to just be this evil, wrong thing that people identify with solely because of their personal moral lack.
Granted, unlike most, I don't think these clips do much to make the movie look good, as it seems incredibly over-the-top and on-the-nose, but the rot that births mass shooters and reactionaries is not moral in nature. Capitalism, technological innovation, and social change have converged on a moment where people can be both part of a generalized overclass (i.e. straight, white male) and yet absolutely miserable because whatever material advantage their intersecting privilege markers may be granting them do not actually result in a better, more fulfilling life, thanks to how atomized and antisocial so much of culture has become. There is a decently large class of people that have intrinsic advantages yet have few to none of the tools to actually benefit from them, and a million ways to further isolate themselves into self-selecting echo chambers where they can egg each other on into more and more detached, "pure" visions of what they think is happening in the world.
This is not to deny that there are genuinely bad, unsalvageable people that affix themselves to these movements, especially in the leadership ranks, where ruthlessness and interpersonal cunning seem inevitably to bestow advantage. Mike Enoch, one of the biggest alt-right podcasters, has a history that suggests he talked himself into the ideology partially because he just really loves being a contrarian dick.
But there is also a reason that these ideologies, which have been kicking around the American underbelly in one form or another for decades, are finding traction now, and I think it has a lot to do with how our various systems of privilege have changed in their outcome as the overall economic and political system have streamlined themselves into vehicles that are hyperefficient at distributing wealth and benefit into the hands of a select few.
That fact, in combination with the decentralization of culture via technological change, has created a situation where the remaining 98+% of people are scrambling for cultural space and attention. This has been a boon to marginalized people, who have been able to lift themselves and their culture out of the underground and into the mainstream, but that (clearly good) trend has the unfortunate side effect of pushing aside and diminishing the sense that there is some grand, coherent, central cultural project to which privileged people not sharing in the narrowly-distributed bounty can feel tethered. (Personally, I would also argue that the extreme dumbing-down of culture, via corporations' relentless and inevitable push toward the lowest common denominator, also contributes, by rendering what remains of the hegemonic culture extremely hollow and vapid, but I'd need more space to expand on that.) This also dovetails quite nicely with our country's rather appalling mental health services, and the destruction of communal spaces that can give people the sense of belonging that is central to mental wellness (a separate factor, for it's simply not true that all of these mass shooters are mentally ill).
This is essentially what every person who deradicalizes from these movements says, in one way or another. They were in a place where they were lost, and they found community and belonging in these movements. This does not cover every denizen of these reprehensible spaces, as some really are just unmitigated bigots from the word go, and others are hucksters looking to make their name. But it does explain a palpable chunk of them, at least in part. This movie, in what looks from the clips to be a rather blunt and artless way, seems to depict that path rather frankly, albeit in an earlier, pre-technological era. It's trying to do a King of Comedy meets Taxi Driver by way of Network thing, and it looks like it's basically a clumsy script leavened by some good acting.
But the act of depicting that descent is not, in and of itself, immoral, nor encouraging of violence. You have to be able to deal with these things frankly, and that includes dealing with the fact that this shit often comes from an effable place while trusting that the vast, vast majority of people understand that violence is bad and that action taken from a film like this should be directed at fixing the social mechanisms that spur people to do this kind of stuff in the first place.
It's neither liberal nor Leftist to argue from the position that explaining narratively how someone reaches a place where they do a bad, horrific thing is tantamount to excusing or encouraging it.