“I still believe that there must be some nefarious motive to be a bona fide apikorus, not just a matter of innocent beliefs that do not ever translate into actions.”
The pashtus of the Rambam is not like that. If you find me a source, then we can talk…
“Why did Avraham not daven for his son Yitzchok to try to save him from the Akeida the same way he davened for the chotim of Sdom? Was his son any less worthy?”
I think the difference is that by Sodom Hashem clearly said this was a punishment, but by the Akeida He simply stated it as a tziyvuy.
“Nevertheless, in the end, the maskana seems to clearly be like I have been writing here all along, that menschlachkeit is the ikar.”
Perhaps, but we still celebrate Avrahom’s willingness to sacrifice everything (including his reputation for mencshlichkeit throughout the world) in order to do Hashem’s will. We still beg Hashem, to this day, “just like Avrahom suspended his mercy from his only son, so may you suspend Your wrath from us…” (from the teffilah right after the Akeida, although I don’t have it front us me so it’s probably not exact). We extol Avrahom for suspending all sense of decency to do Hashem’s will: it seems to me that this is a clear proof the ultimate good is following Hashem, no matter what.