I was just talking with some friends recently about an instance of this: distilling, which is still federally illegal in the US for the primary reason that it provides a lot of tax income if you charge for licenses and tax sales, which is incredibly frustrating because it's easy and safe to make yourself high-quality liquors at a fraction of the price that you'd pay at the store and have a fun hobby to boot.
(pedants: please don't bring up safety issues - it's trivial to realize with five minutes and internet access that distilling isn't significantly less safe than many other unregulated activities in the world as a whole)
This isn't grounded in reality.
Alcohol itself is already dangerous, yet we've managed to figure out how to build cultural elements that mitigate the risks a lot.
You can already buy huge amounts of high-proof alcohol for cheap after you're 21, and most underage kids know someone who could get it for them anyway.
And it's already legal to brew your own alcohol - it's fairly easy to get up to 20% ABV with wine.
And I don't know where you got "unregulated" from. I certainly didn't mention anything about that. Alcohol is already regulated quite heavily - you can't give to a minor or sell without a license, homebrew or not - and legalizing distillation wouldn't change that.
You need to do some research, because you're clearly not familiar with the legal and social environments of the US, at least.