But yet in the D&D universe, "Good" and "Evil" are tangible things. You can have a bottle full of "good", you can have a keg full of "evil". A strong enough wizard can make a big ol' vaccuum cleaner and suck the "evil", or "good", out of someone without altering their life philosophy, memories, opinions, or worldview.

A Marut, a Devil, and an Archon are all lawful, and are all assholes. Neutral. Evil. Good. All three will knowingly harm an innocent, if they felt it necessary. All three do not harm an innocent, if they do not feel it necessary. They're all more lawful than good/neutral/evil, but they still exhibit that other alignment somehow.

If someone held a serf contract for a person in debtor's prison, and the debtor ran away, and the contract owner asked for help, all three of them would go "back into slavery you go, little mortal." Because keeping contracts is important (Marut), because the contract is a deal made (Devil), because following contractual obligations helps society (Archon). The action itself is the same, the result is the same, even the intent is nigh the same: Keeping the contract. But for one to do it is Good, and for another is Evil, and for another is merely Neutral.

D&D alignment systems don't work well, but if you can get a pot of "evil", and make anyone who drinks it evil, then suck it out again, with no long-term effects on the imbiber, then "Evil" vs "Good" is no more personal and emotive than "heat" vs "cold". You can put on a mantle of cold resistance, and you can put on an Axiomatic Holy sword, and then you can pull the Holy out. It's just a fundamental force in D&D.