How do you make sympathetic yet villainous outcasts of society without turning them into special snowflake sues?
I've been reading a lot about historical pariahs (Dalits, Jews, Burakumin) and school shooters
>>55201603
Make them relatable to your players, aside from the whole 'taking over the world', or whatever their evil plan is part that is.
I don't know what you currently have in mind, besides that you want to make an outcast that's sympathetic, nor do I know what your PCs are like, so I can't do much but offer vague advice.
Witcher's Scoia'tael are a good example.
bunch of minority races that had enough of being treated like dirt yet go ape shit crazy and perhaps too far in their quest for justice/vengeance/equality.