Which is a major reason why "hard man making hard decisions" is a really bad idea; that's exactly the attitude it produces. Even if a person starts out genuinely meaning well, they will become warped by it.Just from what is shown in canon RBC really does believe that anything Cauldron does regardless of how morally or ethically dubious is justified because they are working to save "all of humanity, everywhere". She run on the twin ideas of "hard people making hard decisions because they are hard" and "The ends justify the means". Moral, ethical, and even legal boundaries don't matter to her.
Once she started doing all those horrible but "necessary" things, it became emotionally necessary that those things be necessary. Because if they weren't, she's done all those awful things for no good reason at all. And once she started thinking like that it was inevitable that she'd talk herself in doing awful things that weren't even necessary by her original standards, and down the rabbit hole she goes until you have her canon version.
It's literally something used by cults, extremist groups and the like as a form of psychological manipulation; people become very emotionally invested in the cause once they've been pushed into committing atrocities for it. She just did it to herself, instead of somebody doing it to her (except possibly Contessa).