Hamas is labeled terrorist because it was assigned the label by Israel.

Hamas is terrorist only as much as one terrorist entity is credible to decide exactly which groups or factions are terrorist.

More generally, terrorist simply is a label states assign to their non-state enemies.

By the same standards, the Continental Army would be terrorist, as would be essentially every belligerent that has engaged in anti-colonial struggle.

Regardless, it should be concrete facts, not abstract labels, that are used to support arguments and conclusions.