Many advocates for legalisation will show how it is expected to reduce the overall harm from the drug. It will be interesting to see if this plays out in practice. I for one am hopeful.
US national laws are certainly a different case, but the debate is hardly "stifled".
Does the Netherlands not count?
Consumption and carrying small amounts is tolerated, police will not take any action and public attorneys never prosecute these cases.
But production is illegal and besides two small plants in your home, completely not tolerated. If you get caught with say 10 plants they're destroyed with few other consequences. If you get caught with a more considerable production however, you get prosecuted.
A lot of softdrug related crime isn't connected to consumption but rather production. The Netherlands isn't a good case study for studying effects on that kind of crime etc.
Same with many other drugs like xtc. Consumption is rarely criminally targetted. Production is. Virtually ever farmer in the south of the country gets approached by drug producers, there's a whole undergeound web of crime, black money, corruption etc.
You'll have to wait a while for the case study -- maybe until the US itself legalizes.
It's true that those businesses who benefitted from the regulation stand to be making serious money, and I suppose that is different from the situation in the Netherlands in a major way.
Production is only illegal in the same way that tobacco production is illegal - you have to be licences to produce and sell cannabis products.