Circumstances matter!
If the "one" (or "few") CHOOSE to make the sacrifice, then that is noble and good.
If the "one"/"few" is attacking the "many," then yes -- it's self-defense.
If the "one"/"few" are not attacking, and the choice is not made by them, or not made freely, then NO. "A couple of you must die so that many of us will live," is NOT a viable argument, IMO.