does this repetition of aggression in boo radley's past make him more or less of a sympathetic character?

I think Boo is a sympathetic character. In his youth, the other boys were sent to reform school where they learned a trade. Poor Boo was stuck locked in his father's house. Despite the abuse inflicted on Boo, he is still a gentle soul who watches over Scout and Jem. His violence was directed against Bob Ewell who was trying to kill Scout and Jem.