Even if he hadn't, it seems odd to call him a "do-gooder" when he can't be said to have done anything good... No, you are being very harsh. Judges are obliged to administer the law, and that is what he has done in this case -- so the law needs changing.
Even if he had said how sad it was, what good would it have done? Maybe alleviated his conscience, but perhaps too in that he could be said to have been trapped by the law and the case presented before him. From my admittedly limited experience, judges can an do express regret that they can't pass a higher sentence, but that is when they're commenting on what the charge actually was: "Sadly what you are guilty of isn't punished significantly enough in my opinion," or that sort of thing. Legally, I'm sure this is right, she is innocent of manslaughter -- and doesn't that mean that it would be presumptive of the judge to comment on that ?