and many really nasty people had redeeming features, even if that was just loving their budgie or looking out for their friends.
Sure. Agreed. I'd even go a step further that on earth, where we live, there is no such thing as "evil" in a theological sense.
But this if Faerun and, in the world of dragons and magic spells, gods and souls are real. Shar wants me to do evil acts. If I do evil acts I will be rewarded with power from her and also be blocked out of certain actions.
And of course alignment should open up and close off certain conversation threads. As should background, class and race. Why should halflings have the [drow] conversation options?
Ironically, Pathfinder is closer to the spirit of D&D than is BG3 right now. (even if I prefer 5th ed to 3.5)