That's true, and it's the stupidest part of their platform. I'm really not sure how they rationalize it in the context of the Constitution, although it makes sense in the context of absolutely minimal government (which isn't what the Constitution is about; the Constitution is about limited government, not about anarchy). You could call me a Constitutional libertarian perhaps, but I am not a Big L Libertarian.
I'm a little-l libertarian too.
The Libertarians should change their name to the Radical Minarchist Party, just to be honest.
Or they could call themselves the Smurfs. After all, they have fanciful imaginations and a tendency to turn blue.