[grandalf]

The point of a terrorist attack on the subway would be to get the subway closed for a while. Every day it is closed, the city suffers economic damage.

The point of a terrorist act causing loss of life is to create the fear that will cause economic damage, not to somehow wipe out lots of civilians.

In a war, the willingness to kill civilians is proportional to the need to do so to make an impact on the opponent's will to fight. Obviously nobody would prefer to kill civilians over combatants, but all militaries will do it without hesitation if circumstances dictate.