You're assuming that moral propositions are heuristics or a utilitarian optimization problem, and not moral facts that are simply true or not true. This is still a contentious debate, and not the only possibilities either.
In this case, the answers to your questions depends entirely on what the moral facts are. For example, it may be morally impermissible to take a life under any circumstances, which answers many of your questions quite clearly.
I get that this doesn't have the thrilling clarity of some sort of moral fundamentalism. But that's my point. When two groups with different absolute moral beliefs conflict, our options are negotiation or murder. People like the El Paso killer clearly favor the latter. To me that's a sign that however much people hold absolute moral beliefs (and I hope it's relatively little), they should talk about it in utilitarian, relative terms.
See the Categorical Imperative, and also a Proof of the Objectivity of Morals: https://www.reddit.com/r/philosophy/comments/3etl9b/a_proof_...
There are very good reasons why most philosophers are moral realists.