The labeling of groups as "terrorist" is intended to justify authorization for military action against those groups, where, prior to the Global War on Terror, state affiliation or outright sponsorship was typically needed for a military response.

Do you think that's a different understanding of the situation than the one that the state currently has?

Is it not "legitimate" in the same way to kill terrorists?

I am not an expert on the legalities. My impression is that, if they are terrorists, you kind of have to catch them in the act, or preparing to act, or providing support for actions. An army, in wartime, can be attacked in broader circumstances.

Corrections welcome if I am wrong.

The US has murdered around 220 people at sea over the last year for the act of travelling like they are "narco terrorists".