Vietnam was a curious 'war of not', which excelled at turning the trivial task of crushing an inferior opponent, instead, into a convoluted engagement of human sacrifice where 'rules,' ostensibly to contain the conflict, were created to perpetuate it.
It would be very naive to believe the lessons learned during that time frame have not been applied to modern conflicts. While it is true that smaller forces and insurgents can be squirrelly and hard to pin down, I find it rather hard to believe that we have not caught these people, yet.
Apply the same logic to the drug smuggling operations and the gang networks in the world. While I have no doubt that there are good people in law enforcement and elsewhere, who want to put a stop to these things, it would seem that - much in the same way as Vietnam, it has been deemed more valuable to perpetuate this conflict, rather than allow one party or the other to act decisively.
To organizations with secret slush funds and the authority to make records disappear or become national security matters, gangs, terrorists, activists/agitators, etc are all closer to being an asset than a threat or liability, particularly if those in such positions are no longer aligned with our beliefs in law, justice, and morality.