Dear Paul, I'm no ethicist, so I can answer you only from my intuitions. Firstly, I believe that more and more people are actually becoming more utilitarian and so subscribe to the view of the "objectively greatest benefit". Sadly, the lack of ethical education often results in their subscription to a primitive egoistic conception of "greatest overall benefit", i.e. as more people go utilitarian, less people think in terms of ethical rules instead of the calculation. This might be one of the reasons why the world is a mess.

Secondly, I think we should distinguish between the situations in which one might sacrifice themselves for others. My conjecture is that maybe there are some fundamental cases, where reaching the benefit of all is impossible, so in such situations we implicitly expect the agent to sacrifice themselves. But the vast majority of situations is not of this echatological sort, so it's both possible to reach the benefit of all and the sacrifice is not expected. I believe that if this is true, this means that our moral culture draws *a lot* from the Christian ideal, for good or for worse. This is just my intuition, though.

To answer your thought more directly, I would say that indeed there are many ethical rules which rationally make little sense, but maybe morality shouldn't be limited by rationality only? Maybe this is the reason of this profound-altruistic approach of some people?