Libertarian's are typically small government. They adopt those policies from the standpoint of personal liberty though. They believe you should have the right to smoke, believe, say, or sleep with whatever or whomever makes you happy so long as the consequences of your actions are mainly yours to bare.
The Libertarian social platform is far more leftwing than the Democrats (if you can even call Dem's left wing these days). What they typically are not is progressive. Libertarians were the first political party in the nation to adopt same sex marriage as an issue, in the 70's. I'm not that old and I've been around long enough to have heard Democrats call them insane for it.
That said it would be against Libertarian philosophy to use the power of the government to punish say a caterer for refusing to cater a same sex marriage. That is usually where the Dem's and Libertarians part ways.