The crux of the matter is laid out in this verse, but only part of the argument is visible.
Jesus is presenting a false dichotomy: He asks whether one does good or evil on the Sabbath, but that was never the question. Sabbath rules were promulgated by the priesthood and enforced through social approbation. There was never a question of right or wrong. What was lawful on the Sabbath was whatever the person in authority had decided could be done.
While it’s unclear whether miraculous healings were specifically ruled out under Sabbath law, the various activities taken by healers (fires, incense, bell ringing) probably were. Further, Jesus is neither saving a life nor killing one, but offering a silent healing which is arguably a good thing and something one might expect to be appreciated on the Sabbath.