The legalization vs prohibition arguments are fairly standard. Idk if it needs to be rehashed here.
To address your point of inadequate police I will counter that no matter the amount of policing you will never get rid of the black-market. To that point the 'war on drugs' has been a failure.
Yeah, I don't wish for a re-hashing either. The American 'war on drugs' has been a failure, but that was always just empty bullshit. I think with sufficient policing you'll get rid of the black market, but there are many factors to consider when deciding if that's a good idea.
Ah, the old "it wasn't real prohibition" argument.
Sure, we could go full Sharia law and the like and probably eliminate 99% of it--but at what cost? Do you really support such draconian measures and the society it would produce? Fighting human nature is usually a losing proposition. Almost nobody has the balls to do what's necessary, and when they do go full Duterte, you have these pesky international NGOs complaining about "human rights violations", death squads, show trials, erosion of democracy, police brutality, planted evidence, corrupt judges, false convictions, etc.
Too simplistic.
The obvious negative consequences of legalizing cocaine are pretty significant compared to a torture chamber or two, and you don't seem to be discussing them.
Even with cocaine illegal, you could also call this sole consequence of inadequate police resourcing.