On one hand, I fully support Magneto being angry. I think the audience as a whole has seen an incredibly sympathetic view that makes the anger not only understandable, but entirely relatable.
On one finger on the other hand, yeah, humankind seems largely possessed by a Sentinel virus that's making them act in ways that are undoubtedly continuing to bring harm and death among surviving mutants in their darkest hour.
With the other four fingers on that other hand... ehhh we're back to what appears to be genocide right now.
I'm a big Cyclops was right guy, but my interpretation is that Cyclops is about having co-existence without requiring humankind's approval or cooperation. Mutantkind determines mutantkind's own future. Magneto still needs a moment to speak and articulate where his anger is taking him right now (we've not had any chance for him to articulate his thoughts), and that "one finger" that accepts that humankind is kinda acting way out of turn (even if against their will because, y'know, Sentinel takeover) is making his actions feel acceptable to me under the "Cyclops was right" doctrine. Because under "Cyclops is right," I do think mutantkind has every right to fuck up whatever wants to fuck them up, and this counts. But you know, there is an element where a lot of these Sentinel-turned folks are kinda turned against their will and might not otherwise outright harm mutants.