The stronger arguments for me are those that point to the manifest failure of prohibition to achieve its own stated ends. The experience of alcohol prohibition is strongly indicative of the general failure of prohibition. The failure of price controls also seems related - full out prohibition is in some sense a special case of price controls with the government attempting to set the price astronomically high (with jail time being the price the government attempts to set for consumption). Given the lack of evidence for prohibition being an effective strategy, the burden of proof should be on the maintenance of the existing regime. That's even without looking at the clear harm caused by the current approach.

The recent CATO report on the success of decriminalization in Portugal is a recent piece of good supporting evidence for the failure of criminilization. Given the political climate, asking for randomized trials is demanding unrealistically high standards of evidence. Isn't one of the goals of this whole rationality project to be able to make the best possible decisions under uncertainty?