Okay so here's the thing. You know how dragons, giants, and gelatinous cubes are not just things that happen to not exist, but things that cannot exist in Earths physical conditions, and if the laws of physics clearly affecting your characters were applied to them they would just instantly die? Alignment has a relationship to real life ethical reasoning that you are going to find very comparable to huge sized monsters' relationship to the square cube law.
It is not a coincidence that four of the five authors who Gygax borrowed the concept of alignment from were Catholic, that Baator and Celestia are taken directly from the Divine Comedy, that the original writeup of holy symbols only gave the choices "wooden crucifix", and "silver crucifix", and that alignment makes perfect sense if you accept the moral theories of Aquinas and Augustine.
See here's the thing: In the model of human minds used in the specific form of Objective Morality that I consider relevant to D&D, it is 100% of the time the case, for every living sapient being that has ever existed that having an alignment causes wanting things. If you could somehow cancel out someone's alignment, they would stand stock still and stop breathing until they suffocated to death. There is no such thing in this model as having a goal and then choosing a code of ethics, people only have goals because they have codes of ethics. (Saint Augustine specifically claims that people who hold any of the eight non LG alignments don't actually have Free Will.)
So in this model, a Universal Ethical System (which is one of the components of the definition of Objectivity in this case) must answer the question "What should I do?" with the exact same answer, no matter what someone's actual goals are.. The reason this "makes sense" is because it's explicitly a religious argument with an assumed teleology for all sapient beings. Humans (and elves, dwarves, and orcs) are tools they exist to do a job and ethics is the field of figuring out how that job applies to seemingly irrelevant situations.
And while nobody currently writing editions of D&D actually expects you to ride that train, the shape of alignment that was written into 1e, was written by people who basically thought that was how the real world worked. You can discard those assumptions, but you're going to have to do a ground up rewrite of how alignment works.
I do not think it is a coincidence that these statements are all perfectly compatible with the philosophical claims made by Gygax's specific religious denomination at the time he was writing D&D. They're also eminently gameable, which has allowed them to persist under writers of different creeds.
Planescape I believe. Maybe Forgotten Realms wall of the faithless.
Neurotypicality and mental illness are orthogonal to what alignment you are. There are explicitly multiple creatures with alignments that don't even have minds. Nothing is stopping our inverted pain receptor person from being LE.
I kind of get the impression that the religious orthopraxies of Hellenic paganism that informed the myths that all D&D gods are based off of, do not actually take the position that the gods have free will at all. The god of plagues can't just stop giving out plagues, you can just make sure that he gives the plague with your name on it to someone else.