If it were just Ianto I'd agree for a number of reasons (although since they wanted us to suddenly believe that Ianto's death was a big enough reason to turn Jack into a grandchild killing shell of his former self then personally I'd like some indication that he didn't just get over it the minute the plot no longer required him for that role),

Ha ha. They didn't have any indication of that he'd feel that way before the actual death happened. The chance of doing it afterwards? 0 I reckon. I actually think Davies came up with the 'Ianto's death necessary to have Jack kill the grandchild thing' after the event.