Examples: LG Paladin sees all creatures from Avernus as monsters, has no problem killing 'innocent' tieflings on sight.
Ah yes the classic 'the good paladin is actually the evil one' trope. Seriously it only works if you abandon all reason, try to use wordplay to 'game the system' and have no common sense imo.
Good and evil are true concepts in dnd. Murder is still evil, regardless of whatever the one doing it believes it or not. Killing unarmed civilains regardless of race is kinda frowned upon by good aligned deities. Neutral ones could be ok with it depending on the curcumstances under which they occur.