The Doctor has a lot of points in his ledger on the side of "Not going for the practical solution that involves deliberately sacrificing someone else," allowing him to look nobly griefstricken when someone else saves the day with deliberate self-sacrifice. It was grimly fitting with Torchwood's massive collateral damage record that the final solution involved forcing someone to be the sacrificial lamb, but making the lamb in question be Jack's pastede-on grandson doesn't make up for his having been a part of handing over a dozen orphans forty years back.