Saul was a Roman citizen, and there is evidence that he had connections both with the Herods and within the imperial household in Rome. He wasn't "defending Judaism"; he was collaborating with the Romans and the puppet government and high priesthood in Jerusalem to root out subversives.
Fighting Christ Himself is a tough fight.
"Christ" is the Greek translation of the Hebrew word moshiach. Since Jesus wasn't the messiah, I'm not "fighting 'Christ' himself". My opposition are those who, believing themselves to be acting in the name of a Jewish rabbi who died 2000 years ago -- and who was himself Torah observant -- try to persuade Jews to abandon the Torah.
As others have said, I have no beef with Christians who do not try to proselytize us. Live and let live.