Watch the Pulpit?

I've been reading Freedom From Religion, and recently spent a little time talking with the author about the book.  The basic version of the book is argument for the conclusion that it is appropriate for police agencies to monitor speech in religious contexts where there is reason to think the religious speech may incite crime.  In other words, urging murder and mayhem is subject to surveillance whether or not in a house of worship.  The book is selling well, and the reviews suggest that it is highly controversial.  It is nicely written and a relatively smooth and fact read, but I missed the highly controversial part.  I am not much of a fan of state surveillance of speech to start with, but I still don't see why the suggestions are particularly troubling.  Limiting the discussion to the United States, I learned that there is some hesitancy on the part of the FBI and other agencies to involve themselves in monitoring speech in houses of worship.  This surprises me.  As I recall the trials connected with the Sanctuary movement in the 1980's the FBI and others had no qualms about infiltrating religious organizations or attending (undercover) meetings in religious houses.  (Sanctuary was about aiding refugees from the wars in Central America.)  Or, following the invasion of Iraq, the FBI seemed to have no qualms about infiltrating and monitoring Quaker anti-war groups, meeting in houses of worship.  I suppose there has been some great change in the climate, or is it just a facade?  Setting aside the historical issues, I don't see why religious speech should be treated with more care than political speech.  What sort of argument is there for such a difference in treatment?  Is there something special about what happens in a house of worship?  The Supreme Court suggested not in the Smith case, in which a worshiper was fired for full participation (eating peyote).  Is it some sort of slippery slope theory -- if the police start monitoring some church talk, then soon enough there will be pressure forcing the police to watch the folks in the christian churches?  If someone is talking about killing other people, whether because apostates or because they provide abortions, that is just the sort of talk that deserves monitoring.