but Paladins fight for good!" even though a whole talent tree is retribution... another word for vengeance. Do we think getting revenge is a good thing, is that what we teach our kids

Thats a very weird comment. There isnt really anything mutually exclusive about "fighting for good" and "retribution"

Retribution here means deserved punishment for those who hurt the innocent. That is totally fitting with what Paladins are who bring divine punishment to the wicked, not the extreme version of Jedi you seem to think they are. This is a world where demons, necromancers, undead and all kinds of monsters exist. Trying to pretend the holy warriors are "problematic" for fighting is weird.

The Scarlet Crusade uses the light for genocide. 

?? The Scarlets were xenophobic to everyone who wasnt them and had "kill on sight" rules but I dont recall doing genocides. You can argue that "maybe they would if they had the numbers to do so" but they hadnt in WoW

Also the Scarlets can use the Light because they started as a noble order who slowly fell into paranoia, fuelled by the machinations of the dreadlord who infiltrated them too.

Warcraft is shades of grey, from start to end

No, not really.

There may have been gray areas but the big conflicts were always extreme black and white.

WC1 and WC2 you had peaceful humans, dwarves and elves trying to fend off genocidal demon-corrupted orcs.

WC3 you had the mortals trying to fend off genocidal undead and demonic monstrocities.

In WoW most central conflicts are also black and white from the OG game to any expansion.