That's not an iron-clad argument, as legal gambling can still have mob ties, and tacit permission of some illegal gambling might still permit some level of oversight. And of course, legal gambling doesn't ensure reasonable or effective oversight or regulation.
By establishing known, legal, and possibly even bettor-favourable facilities or systems, gaming becomes something which might have some level of oversight. The increase in online gambling does severely cut into this argument though.
Another challenge, in the U.S., comes in the form of reservation casinos which can operate independently of other state prohibitions on gambling, which means that total eradication is at the very least difficult.
But that is an argument which might be made in answer to your "why not just..." question.
(I'm generally not a fan of gambling in any of its various forms. I'm cognisant of its pervasiveness and some of the worse aspects of it.)
Though the pre-2018 situation was that personal (that is, not intermediated by a company) gambling was legal, which provided an out.
Again: I'm positing the argument, I'm not advocating for it. And it does appear to be counterfactual.
Of course doing it in a way so it can't be tracked keeps the IRS ignorant, which is a big deal to many people
Guess it's good my luck was terrible in Vegas or I might've inadvertently committed tax fraud. Though now I'm curious if I had won a few hundred dollars would there have been tax due?
I'm pretty sure it's tax free in most countries.
I strongly suspect that one element of legalisation is that it normalises the activity, which lowers all sorts of social and psychological barriers to participation.
Another is that it creates self-organised self-interest groups. This is actually a really great way to ensure the longevity of governmental programmes, with both positive and negative examples: welfare systems such as Social Security, Medicare, and the ACA in the US are all immensely popular with the elderly, a staunch voting block, to the extent that its general trend toward conservativism doesn't fully mute interest in social welfare. The military-industrial complex is another, and a recent discussion I'd heard of the Inflation Reduction Act highlighted the constituencies built in to support it even in deep-red southern US states.
In the case of legalisation of gambling, drugs, and sex work, what had previously been the purview of criminal gangs now becomes "ordinary business" (though the thought occurs that the distinction between the two may be less than is commonly understood). To the extent that established businesses prove to be highly effective at defending even the most indefensible of practices (tobacco, alcohol, asbestos, lead, plastics, fossil fuels) is well established, and the risks of that path should be strongly considered.
Another option is to decriminalise rather than legalise a practice, but focus on policing the most problematic elements of the practice. That might be the provider side (as with drugs and gambling) or the consumer side (as with sex work, targeting johns), or on going up-market and tightly limiting or prohibiting private aggregators (e.g., pimps, drug lords) rather than focusing on low-level actors (streetwalkers, individual workers, street crews within drug operations).
State-operated operations (gambling, lotteries, alcohol and tobacco sales, drug distribution *with integrated treatment), is another option, though it too isn't a surefire solution. My view is that lottery programmes in the US are out of control and a net negative, though in part that itself reflects the public-private partnership in the operation of many of these.
Thanks for the correction.
The solution to this problem would be mandatory sex worker licenses and mandatory yearly counseling that acts as an escape path for trafficking victims.
There are many women police officers in vice and many means with which to tackle sex trafficking, with or without the testimony of specific victims (bearing in mind that sex trafficking almost always involves many victims).
Yearly contact seems ... sparse... there's more sense to be had in mandatory weekly or fortnightly STI checkups, etc. which incorporates contact with trained medical professionals familiar with the ins and outs of te game.