Money is power and you are underestimating how much power money has. To do research you need money and that money most likely needs to come from big companies. Big companies need access to bank accounts, credit cards and payment systems. Guess what happens if they piss off the US government. Every bank is directly or indirectly connected to a banking license in the USA and no bank wants to risk that license.
I did not look into this recently but not too long ago it used to be a thing that no bank would serve legal cannabis businesses. Your bank gets a ‘visit’ from a government agency and suddenly you are a cash only company. Because the bank can choose whether or not to serve a customer and they ‘choose’ not to risk their bank license by pissing of the government.
Oh and I’m not from the US btw.
What I meant is for example: ‘cannabis does not cure cancer’. There is no evidence that it does because there is no research. If I’m not allowed to say that it can cure cancer then somebody else should also not be allowed to say it does not. The only evidence we have today is anecdotal evidence of people claiming it helped them. And they have no problem telling because there is no financial motive not to tell and it saved their lives or made it less painful.