The only reason military should exist is to perform such life-saving, not life-ending, missions...

What if you were Ukrainian?

Seems consistent. Ukrainian soldiers are performing life saving missions i.e. defending their citizens from an unprovoked attack.

then the military would also act life-saving, since they are defending the attacked country

Then the military should have stopped the country from trying to join NATO, avoiding the invasion of Russia and saving countless lives and homes.