Lyxen
Great Old One
Evil and Good don't exist in real life as objective concept. In some RPGs, they can exist as a scientifically testable concept (I cast "Detect Evil" on him. Does he flash red?) and be objective.
In such a concept, I don't see our real life conceit that we can't be "evil" or "good" without the ability to choose being applicable. Of course, we'll put murderers in jail and we won't kill their children to spite them, but that's not necessarily something generally applicable, it's just a legal concept (and maybe even only a Western legal concept).
Let's imagine a setting in which "Good" is "what the good gods decreed to be good" and "Evil" is "what is forbidden by the good gods". There is not necessarily an overlap between what we deem good around the table and what the good gods would think. If you're playing in say, Biblical Egypt, you're supposed to think it's "Good" to threaten to kill the first-born of those who wouldn't smear blood on their door, even if the first-born is a little baby without ability to make moral choice (or have any say in what is smeared on the family's door). In such a setting, the infant in his cradle would register as Evil when a detection spell is cast upon him. If you're playing in an Aztec setting, you're expected to consider that it's OK to sacrifice your foes to ensure the continuing existence of the Sun, which would be labelled as good, despite our moden views being more nuanced on these practices. It might not be for everyone (not all settings are equally palatable), but after all, part of the roleplaying appeal is imagining how a character would think, not how we would fare if we were put in the characters' shoes.
Yes, but fortunately D&D provides an objective definition of evil in the game, which was necessary, especially in previous editions since actual mechanics depended on this. Now, it's mostly gone anyway.