Well, in fact it would be highly helpful to separate the claims here, even though the factual part is uncontroversial, because it makes it clear what argument is being made, exactly.

And in this case it's uncertain/controversial how much power actually changes behavior, who it changes, how reliably; and this is the key issue, whereas the moral concept that "the behavior of killing everyone who disagrees with you, is wrong" is relatively uncontroversial among us. So calling this a moral claim when the key disputed part is actually a factual claim is a bad idea.