> ...if you want to support a political candidate...
That is the false choice, also commonly found in the form "the lesser of two evils" or "the most electable".
> That's the only way to torture this analogy into shape.
I can think of a better one, better because it actually happened. An anarchist starts making a bunch of noise about how 3d printers enable individuals to produce extremely low quality guns in the privacy of their own homes. Liberals are outraged, propose legislation to ban such activity - then float the lead balloon of 3d printer technology regulation. Like the burning garbage analogy, externalities are used as justification for liberty curtailment, but unlike burning garbage - such externalities are not a certainty (in fact home firearm production has been legal for a very long time). The liberal's real beef is with the threat to the state's authority, the more often the state's regulations are sidestepped - the weaker it appears.
So the short answer is this: liberals, like conservatives, are fine with private activities that don't threaten their world views. Unfortunately liberals have a very detailed idea of the way the world should work, whereas the conservative imagination doesn't go much further than approved penis destinations.