My copy of the second amendment says "shall not be infringed", so yes. The possession was legal; the use was NOT.
Anyone who cannot be trusted to be armed should not be running around loose. And all drug dealers should be executed, from street level to mule to kingpin.
And re post 31: execute any government official or employee taking their cut from the cartels.
Re your latter: The entire American landscape is literally littered with CIs (confidential informants) enslaved by the justice system as a result of mostly minor drug charges (the true prison population would be likely quadruple if they applied 'justice' equally). Those CIs are now being used to inform upon anyone, not just re 'drugs'. The 'game' is now a self-fulfilling prophecy (i.e., the 'war on drugs' monster, aka the 'prohibition industrial complex', which now extends its tentacles to civil asset forfeiture to feed the machine).
I would argue that the solution lies not in executing those you suggest, but those who have corrupted the justice system.