If the government never abused its authority, I would be much more sympathetic to Kerr's position. Given the facts of prosecutorial abuse, vague and conflicting laws, the ongoing gutting / suspension of habeas corpus, "three felonies a day" -- http://www.threefeloniesaday.com/Youtoo/tabid/86/Default.asp... -- and many more reasons not to rest moral authority on our body of law, I find his insistence that we revere lawfulness to be foolish at best. It's important to stand up to unjust laws.
Leaving aside warrants which are merely held to be lawful (where the true facts, might we know them, show the opposite), it's not just lawful warrants that this technology protects against. Law-abiding citizens may be compelled to reveal private information via totally unjust mechanisms such as National Security Letters. Consider Nick Merrill's experience: http://en.wikipedia.org/wiki/Nicholas_Merrill#Challenging_th...
Also http://techpresident.com/news/24272/nick-merrill-fought-fbi-...
Let's not even get into protecting yourself from the NSA. Any tools which help us resist such tyranny, even at the risk and expense of civil disobedience, are to be applauded. Reserve your condemnation for the John Yoo of the tech world.