You stated a problem: how to get people to agree. You gave your solution to the problem here (my emphasis)

Personally, I think a reasonable first step is to try to restrict ethics to utilitarian approaches. We'll never reach agreement as long as there are people still trying to use rule-based ethics (such as the "double effect" rule). The difficulty of getting most people to agree that there are no valid non-utilitarian ethical frameworks is just a small fraction of the difficulty of the entire program of agreeing on human values.

I pointed out, however, that it is apparently utilitarianism that has introduced the disagreement in the first place. I explained why that seems to be so. So the problem may be utilitarianism. If so, then the solution is to reject it.