It’s bad enough that so many self-declared conservatives, who support personal freedoms and limited government in so many other respects, are opposed to taxing and regulating marijuana. But it’s completely unacceptable for an otherwise stalwart progressive to have such backward views on marijuana. Asked last night whether she supports legalizing and regulating marijuana, leading Massachusetts Senate candidate Elizabeth Warren gave a flat, no-nonsense (and no-common sense) “no.” Several other candidates…