Historically, the problem of "this is just like Hitler!!!" has been the way in which it numbs people to the invocation.
That is, in no small part, the appeal among conservatives of calling everyone from Hegel to Whole Foods a form of creeping fascism. Putting every liberal politician (and a fair number of conservatives) in Hitler Cosplay helped diminish the idea of an authoritarian police state to seat belt laws and smoking bans.
The flip side is that stodgy NYT Op-Ed Writers who casually reject that any fascist impulse exists at all. Everyone from Fransisco Franco to Sheriff Joe Arpaio was just interested in Law & Order. The game of explaining why a given genocidal policy or nakedly fascist aesthetic is actually something different, you idiot, you imbecile, goes right up to the point of denying migrant detention camps along the border and mass extermination of Semitic people in the Middle East and trillionaires doing the "Roman" salute are what they clearly appear to be.
In the end
gets you coming and going.
It becomes a casual invective to describe even the most mildly distasteful political views and a "you're just being hysterical" rebuttal to any policy that is quite literally adopting mass extermination.
While the criticism is on point, I think you're underselling the legitimate dire fear modern leftists have when they see the brutality of the periphery returning home. We have to recognize that - individually - we're incredibly weak in the face of a mobilized police state. And we have every reason to be horrified of The Jakarta Method being visited on LA or Atlanta or Houston, particularly if we're members of that domestic political underclass so often targeted for abuse.
Any opposition must be a unified and organized resistance. But we are also plagued by mass surveillance, structural alienation, and a profound sense of vulnerability cultivated over decades of "War On" maximalist state propaganda. So we're feeling weak, we don't know who we can trust, and we see this horrifying inevitability cresting over our heads like a tsunami.
This isn't a betrayal of comrades abroad but a reflection of our own dismal moral, disunity, and despair. It represents one more hurdle for a modern western left to overcome and should be received as such, rather than used as a bludgeon to degrade left-wing moral even further.
Far better to be awake and aware and justifiably afraid of the threat of fascism than blind to it as the unaligned, compromised by it as the liberals, or enthusiastically participatory as the conservatives.