They’re Ice Demons, born on a frozen world, equipped for the cold. They don’t stand a chance against Torchwood’s weapons.
Jack thinks Ianto is being uncharacteristically vindictive but really, it’s just pragmatism. Jack’s only alive because he can’t stay dead. Anyone else wouldn’t have been so lucky. Ianto intends to make sure none of these creatures gets another shot at killing a human; he’ll take them on single-handedly if he has to, but they are going down.
Termination with extreme prejudice, if you like.
He’s not alone though, the team stands beside him. There’s going to be an early thaw.
TBC in ‘Victory’