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'.
(..) ...to never do again. I have created "something that kills people." And in that purpose, was a success. I've done this because philosophically, I am sympathetic to your aim. I can tell you with no ego, this is my finest sword. If on your journey, you should encounter God... ...God will be cut. Go. (..)2003 Kill Bill: Vol. 1