Weeding out FARC and Shining Path actually did teach valuable lessons which habe been repeatedly reapplied successfully during modern counter-terrorism.
Both where heavily invested in organized crime but are nowadays toothless or non-existant due to coordinated goverment and civilian efforts.
The Best example might be “The Sons of Iraq” who helped to pacify Iraq quite well. The Coalition literally hired local people suffering most from extremists to fight the extremists and it worked like a charm. FARC and Shining Path were pushed into insignificance by roughly the same methods.
Yes, there were “revenge” killings by the “somewhat good guys” against the “really bad guys”. But in hindsight it was necessary to show the “really bad guys” that the tables had turned. As long as the overall violence decreases - deal with it.
Oh, by the way, did you know that the Mafia once was an organized military organization fighting for Sicilian independence? Over the last 200 years they slowly degraded into a bunch of sometimes wealthy oligarchic stock market fraudsters, but mostly pick pockets and low level fraudsters, at most bribing officials for construction jobs, if at all. 40 years ago they killed judges and police officers in the dozen. Nowadays they get beat up if they show up in Palermos shops and demanding the Pizzo (protection money). And the police stands by and collects the beaten gangster afterwards without minding the locals doing local justice. Works fine.