What does free speech have to do with protecting citizens from verbal and physical harm? These zones were established because of past abuses and deaths caused by anti-abortion zealots, not some arbitrary ban.
As Rachel Maddow and others have pointed out, there have been free speech buffer zones established for other groups too, like the Supreme Court itself. Conservatives didn't complain, in fact liked it, when "free speech zones" were set up a blocks away from Bush/Cheney events. But Justice Scalia seems to be missing the point:
“Today’s opinion carries forward this Court’s practice of giving abortion-rights advocates a pass when it comes to suppressing the free-speech rights of their opponents. There is an entirely separate, abridged edition of the First Amendment applicable to speech against abortion. Because, like the rest of our abortion jurisprudence, today’s decision is in stark contradiction of the constitutional principles we apply in all other contexts, I dissent.”Here's Rachel Maddow with examples of other buffer zones:
Here's a nice piece on a new book about Scalia, and just how unacceptably "activist" this guy is, especially about the Second Amendment: