Ruth Marcus, an utterly reliable liberal, and Peter Wehner, a traditional-values conservative, have also chimed in about legalizing pot.  The Marcus piece starts off with something of an apology for being a fuddy-duddy, but goes on to make a powerful case. These paragraphs in particular struck home:

On balance, society will not be better off with another legal mind-altering substance. In particular, our kids will not be better off with another legal mind-altering substance.

As the American Medical Association concluded in recommending against legalization in November, "Cannabis is a dangerous drug and as such is a public health concern." It added: "It is the most common illicit drug involved in drugged driving, particularly in drivers under the age of 21. Early cannabis use is related to later substance use disorders."

And this point, for me, is the most convincing: "Heavy cannabis use in adolescence causes persistent impairments in neurocognitive performance and IQ, and use is associated with increased rates of anxiety, mood, and psychotic thought disorders."