He was not 'sympathetic to/toward' their cause. [=he did not support their cause]
The book doesn't really have any 'sympathetic' [='likable'] characters.
I didn't find the hero in the movie very 'sympathetic'.
(..) but it is peace. I have to hold on to it. I have to try. Although the Kingdom cannot grant you the aid you desire, the King is sympathetic to your plight. I offer our friend Daryl asylum for as long as he requires it. He will be safe here. The Saviors do not set foot inside our walls. (..)2017 TvShow: The Walking Dead Title: Rock in the Road Season: 7 Episode 9