I see both of you having reason here:
The T-word is over used from my POV, and without differentiation.
Insurgents are insurgents, Freedom Fighters (for their country) are Freedom Fighters - and you would be one of them if it was yours-, pirates are pirates, criminals are criminals, and whackos are whackos. We would not employ so many different words if the ppl we describe with them would not be different.
Differences are in: a) Ideology, b) Procedure, c) Motive, d) Goal and e) Association
"Terrorist" has a very close definition, and if you want to use it in broader sense, plz say so, or we will all be misunderstanding ourselves all the time and discussion would be moot.
Personally I would really appreciate if ppl got their nomenclature spot on.