Michael Barone‘s latest column explores the negative impact that results when left-of-center thinkers insulate themselves from conservative arguments.

Liberals can protect themselves better against assaults from outside their cocoon. They can stay out of megachurches and make sure their remote controls never click on Fox News. They can stay off the AM radio dial so they will never hear Rush Limbaugh.

The problem is that this leaves them unprepared to make the best case for their side in public debate. They are too often not aware of holes in arguments that sound plausible when bandied between confreres entirely disposed to agree.

We have seen how this works on some issues this year.

Take the arguments developed by professor Randy Barnett of Georgetown Law that Obamacare’s mandate to buy health insurance is unconstitutional. Some liberal scholars like Jack Balkin of Yale have addressed them with counterarguments of their own.

But liberal politicians and Eric Holder’s Justice Department remained clueless about them. Speaker Nancy Pelosi, asked whether Obamacare was unconstitutional, could only gasp: “Are you serious? Are you serious?”

In March, after the Supreme Court heard extended oral argument on the case, CNN’s Jeffrey Toobin was clearly flabbergasted that a majority of justices seemed to take the case against Obamacare’s constitutionality very seriously indeed.

Liberals better informed about the other side’s case might have drafted the legislation in a way to avoid this controversy. But nothing they heard in their cocoon alerted them to the danger.