I agree - I also think you could have let Ianto live, and have him support Jack killing Steven; putting the boy on the little stand when Jack couldn't do it, holding back Lucy, etc. Because I think Ianto would have known that was what had to happen. It was horrific but it probably had to happen.


Agreed, and remember that Ianto would have had a personal stake in the outcome. If he opposed Jack, he'd basically be condemning his niece and nephew to the aliens. He supports Jack and he's condemning Jack's grandson.
And imagine the aftermath.
Would Jack end up resenting Ianto because Ianto's family is still alive? Ianto would be torn between relief that he didn't have to lose his family, and sorrow for Jack's loss.
GDL and JB could have done soooo much with that.