Nobody today argues that tobacco is anything other than a poison. Ask your doctor what counts as "moderate" consumption of alcohol, and she'll specify a weekly ration that Don Draper would have finished by Tuesday. Buying prescription drugs without a scrip is a serious legal offense, as Rush Limbaugh could tell you.
With marijuana, unfortunately, we hear influential voices telling people that this mind-altering drug is a "medicine" - and a uniquely benign medicine at that, since it comes out of the ground, not from a lab. Legalization is advocated not as part of a strategy to control and restrict, but as a way to engraft marijuana into a normal lifestyle.That last sentence is the key. The legalization of marijuana is part of a deliberate attempt to alter the culture's views of this substance. Unlike the laws regarding alcohol or tobacco, which are restrictive, the efforts to legalize marijuana are attempting to expand access to the drug. And as Frum points out, there are strong Burkean reasons to think that such an approach is is the wrong one to take.