when to limit freedom (revisited)-- in the case of "free speech"

From the opening of Matt Welch's essay in Reason on Elena Kagan, Barack Obama, John Roberts, and "free speech":

He opens by quoting Kagan: "Whether a given category of speech enjoys First Amendment protection depends upon a categorical balancing of the value of the speech against its societal costs." Then Welch responds:

In April, the Supreme Court treated this cost-benefit approach to the Bill of Rights' first proscription on federal power with the derision it deserved...Kagan's claim was a timely reminder that government, always and everywhere, seeks to balance controversial speech against various counterweights: national security, concerns about the influence of money in politics, the desire to protect society from coarsening effects of obscenity...Many, perhaps most, restrictions on speech are popular when they're enacted. The reasons aren't hard to understand. When your overriding goal is to prevent something most decent people find abhorrent...people start to say, "Normally, I'm a First Amendment absolutist, but..."

This is an excellent point in itself-- and also relates back to the recent "furor" over Rand Paul's reasonable points/questions about civil rights legislation.