This. Alignment in D&D, from it's earliest incarnation, is about where a being stands in relation to the ages old, highest level of existence war between the forces of civilized Law and primordial Chaos. Whether you are "good", "neutral", or "evil" just reflects the means you'd use to reach the end of your cosmic side winning. It has nothing to do with relativity or morality, it's meant to define the forces that make up an ages old conflict that is so far up beyond the average person in any setting that they can barely comprehend it. A real world example would be God and his Archangels vs Lucifer and the exiled angels along with him. Your alignment describes the part you play, no matter how small it is.
There's a TON of D&D mechanics that have survived long enough to be included in the newest editions that players thoroughly misunderstand and misapply because so much time has passed since their inclusion that they've been bastardized in a million different ways
tl;dr: almost any question about "why the fuck is D&D like this" can be answered by reading the original edition and 1e handbooks