They're against addiction, and they're against recreational drug use. Agree or disagree, why not take them at their word?
Because the evidence is all to the contrary.
Portugal ran the biggest experiment - 8 million people - and upon legalization, their drug use fell in half. The UK experienced the same thing in the reverse direction upon criminalization of e.g. heroin. The result is consistent with rational views of human incentives as well, so no logical surprises.
People who are pro- drug criminalization are for increased addiction rates. That's what reason predicts and that's what the empirical results are.
Whether or not these people are rational is immaterial to the consequences of their actions. We shall not give them a "pass" on "good intentions" if they lead us down the Road to Hell. The JAMA research suggests they're responsible for a minimum of one 9/11-scale effect every year.