Any use of violence need opposing and competing forces in a market to work.
Judging by the quality of service, it obviously doesn't work when the government has a monopoly of legal violence.
As you mentioned, having people doing it illegally is prone to the creation of a black market. Black markets need to stay hidden so they'll have lower standards and generally a worse experience for everyone involved. If there wasn't any control on these "big guys", eventually someone would come up with a way to broadcast these "big guys" reputation. Someone could easily hire some other "big guys" to keep the other ones in check.
I heart afganistan has no such monopoly, opportunity!
Having a legal and black market operating side by side can mean more quality and variety for the black market. The drug market is a great example where in places a legal market exists the black market can offer better prices, better quality and a variety of strains the commercial growers cannot.
We don't need a black market, we just governments not to get in the way in what they consider legal or not. I think you're advocating for small independent producers vs big monolithic ones (which sounds great, I'm in!). In a world where licenses don't cost half a million, that can be a legal market as well.
> The black market can have higher standards From my anecdotal European experience this hasn't been the case. Eg. If I think about cannabis in Netherland, what you can buy in a coffee shop is generally much better than any black market deal you can find in all of Europe. You can get cannabis from Amsterdam in the rest of Europe as well (amongst the dozen fakes) but it will cost much more.
In a black market you have a higher risk of getting scammed, lower quality and no controls. Online marketplace with reputation systems help a lot but it's still not like buying on Amazon.
The barrier to entry is higher because you have to setup the tools to act anonymously (eg. Tor, cryptocurrencies), you have to worry about stealth and you're running the risk of going to jail. The quality / price ratio goes down pretty quickly. Sure, you're not paying taxes and you don't have to do accounting, but I think the negatives are more expensive than that.
The US governments have a monopoly on violence and sanction self defense and defense of property.
I think in order to avoid open conflict from law enforcement, these types will try to avoid residing at the scene of the crime. Instead, they will rely on referrals for repeat business, while keeping things on the down low.
Who cares about the old lady stealing sweets from the reception candy dish during a bank robbery on a mafia bank?