My in-setting reason for my Guardians for supporting the factions they do is: Hunter -> Dead Orbit -> likes the colors/designs Titan -> FWC -> likes the idea of a huge incoming war, reaction to people seeing visions that drive them mad is wanting to go to whatever place/timeline they saw, cause she's a lunatic like that Warlock -> New Monarchy -> cause they want to remove the Vanguard from power and she dislikes them (and the boring irl reason that it was the 3rd faction and my 3rd character)