Unless you can build some sort of moral truth detector, "simply true or not true" is still a subjective proposition, because it's you believing that. So whatever you imagine the absolute truth to be is mostly irrelevant, in that you need to persuade other people with different viewpoints to behave the way you want. That leads you back pretty to utilitarian optimization problems.

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.