As powerful as it is to know that Jack was willing to let the world go to the 456 if only Ianto would be spared, as a bubble moment in and of itself, it’s so much more powerful knowing Jack’s characterization. Because he is always making hard calls and making sacrifices for the good of the world, but Ianto is where he draws the line.
Jack let Jasmine go with the fairies for the good of the world. This is made more palatable because she wanted to go, but it’s still a sacrifice that makes Jasmine’s mother lash out at him and causes Gwen, Tosh, and Owen to give him the cold shoulder. I think it’s debatable whether or not he would have let the fairies have her even if she hadn’t wanted to go - maybe the issue would have dragged on a bit longer, but barring any other solutions presenting themselves (and the episode makes it clear this is unlikely), I think he would have given her up.
He sacrificed the original 456 victims as well. He knew that he was handing a bunch of scared little kids to an alien, and he didn’t know what was going to happen to them; they could have been dinner for all he knew. This was also not his call to make, but he went along with it because it was made clear that it was 12 kids or the world. He follows orders and doesn’t even try to find another solution.
He sacrifices Steven, his own grandson, to stop the 456, because it’s down to the wire and this is the only solution available. They don’t have time to come up with anything else. And what else is he going to do? Go hunt down a less conveniently available child and devastate someone else’s family just to keep his own intact? Most people would have; we see all the politicians specifically discuss that none of their families will lose children to the 456.
Yet Jack is willing to walk away from the path he’s set himself on of protecting the world, and would let terrible, horrific things happen in the world and to other people, if only it would save Ianto’s life. And knowing that in the context of Jack’s previously established characterization just makes it that much more devastating and really speaks to how much he loves and needs Ianto, and also to the effect the loss of Ianto has on him, despite their relationship never really being discussed in the text very much or taking centre stage at all.
This broke me.
