But in the case in which torture is being argued here there is a threat. And it is from a group of people. And the person being tortured either A) has connections with the group or B) is a member of the group.
If a gang threated to kill your loved ones, or one of your own, then in selfdefense killing them all would be fine by most people I know. Selfdefense CAN target a group.
And the purpose of selfdefense is to protect yourself or your own from being hurt. Thus it is preemptive action. Torture can be used as a preemptive form of selfdefense.