This is, actually, an absurd opinion. Massive civilian casualties are inseparable from war, and you will be hard pressed to find a war without them.

The laws of war are built around, and exist because of, this assumption. They exist to give a framework that sets forth principles by which the loss of life can be evaluated.

Otherwise, by your definition, every warring faction ever is a war criminal.

Yes, the land is stolen. Yes, resistance is legitimate. No, murder of civilians is not acceptable, no matter which side does it.

Would you really hold the same view if native Americans massacred American civilians in the US today?