I have come to understand this story quite differently after practicing family law for about 15 years. Yes, I saw all kinds of ways love and family relationships can go crazy, but after a while I gained a little bit of insight on the kinds of complicated situations that can lead people there. Abraham's relationship with Isaac is a whole lot more complicated than it seems.
Abraham loved his firstborn son, Ishmael, but Sarah regretted the whole surrogacy thing with Hagar. Then Abraham turns the tables on her, and gives her to Abimelech. Sarah comes back from his house pregnant. (Read the chronology of the narrative, leaving out the Lot story in the middle. God says to Abraham, "This time next year Sarah your wife will have a son," and the next thing Abraham does is move to Abimelech's territory & give her to him, Abimelech returns her with a big display of innocence and reparations to establish his claim the child isn't his. Then Isaac is born.) Then Sarah tells Abraham to send Hagar and Ishmael away, and God says, basically, "You listened to Sarah in having this child, now listen to her again."
Then, God says to Abraham, "Take your son Isaac, your only son, whom you love..." Do you see the irony in that? Isaac was not Abraham's only son. Ishmael was Abraham's son whom he loved. And considering the circumstances of Isaac's conception, Abraham was probably ambivalent about whether Isaac was actually his son at all.
I think Abraham obeyed God because he didn't really love Isaac. Abraham resented Isaac. I think it took something as dramatic as this incident for Abraham to even begin to feel any love and compassion for Isaac.
So should Abraham, ethically, have refused? You may all be right that he should have. The fact that he didn't even argue with God about it proves he didn't really love Isaac. God had to show Abraham that God loved Isaac more than Abraham did.