The problem here is you are mixing up "justified" with "reality". In reality #3 becomes #2 and thus we say that those who take position 3 are really taking position 2.It seems that there are three basic positions in this debate:
1) Israel is justified in killing innocent Palestinians to destroy Hamas.
2) Hamas is justified in killing innocent Israelis to destroy Israel.
3) Neither Hamas nor Israel is justified in killing innocent people to destroy the other.
Nobody here is defending (2). Some defend (1) and others defend (3). Those who defend (1) often portray the defenders of (3) as defenders of (2).
In an ideal world no innocents would die. That's not the real world, though. Civilian deaths in war happen. They especially happen when human shield tactics are being used.