Good and Evil

[Hatshepsut]

The ethics of Feudalism, for example, are almost immeasurable in every respect, dependent as they are on the whims of the feudal Lord.

I was under the impression that the rules & obligations were pretty definite on both sides, the problem being they were so frequently honored in the breach. Feudal lords owed protection from outside predators and relief of poverty resulting from factors considered beyond the tenant's control, say if one household's field got blighted but neighboring fields on the same estate didn't. The system may even have been relatively "fair" in theory, if one makes allowance for the limited personal freedom offered, though of course enforcement mechanisms were lacking and lords often absentee. I see their system's lack of practical recourse for the aggrieved, i.e. no police and no central high courts to discipline wayward lords, as more of a problem than the measurability of its ethical criteria.

Their conception of harm would likely have been similar. Remember that humans have undergone very little physical/neurological change over the past couple of millennia; what hurts us now would have hurt us then...

Physically, sure. Having your leg sawn off hurts in any era. My point, which maybe I should clarify, was that medieval societies discounted an activity's harm to individuals if that activity benefited the group. Today we are so much more reluctant to transgress the individual's boundary that we often allow the group to suffer in preference. Take the 2nd Amendment in the USA for instance, a carte blanche for gun ownership rights for which we pay a blood price of 30000 lives annually.

If we look at medieval literature, we sometimes see themes of childhood trauma being stated as the cause of both adult derangement in villains and drivers for heroism...

The Miller's Tale (Chaucer) sprang to mind, but the lass was 18 and the trauma inflicted by Absolon's red-hot poker in the arse an adult one...inadvertently done to the poor sot who just wanted to take a dump! O well, my imagination faileth me at the moment.  

...why wouldn't we also believe there are moral philosophers who have also spent more time analyzing...situations...so as to trust their judgment (supported by facts and reasons, of course) about ethics in the same way that we rely on other experts?

I'm inclined to agree. I'd rather have the pompous professor from Purdue making the ethics recommendations than get them from Bo Gritz, the onetime lunatic presidential contender who wants to take the U.S. out of the UN and put us back on the gold standard so we can rereun the Roaring '20s all over again.