Interesting line of argument, but really beside the point. You are
correct that Leif has taken the wrong line of argument, but you yourself
haven't quite got it right.
Leif speaks as if the government has a right to monitor our thoughts.
Such a stance indicates that we are property of (a|the) government.
Just the opposite is true. The just government serves at the pleasure of
its citizens, and must not be allowed any more power than what is
strictly necessary, if any at all.
For the US, the 4th Amendment applies, and all of the history
surrounding it - secure in papers and effects, unreasonable
search/seizure, etc.
The recent NSA actions (and older programs, too, such as Echelon), taken
at the behest of Presidential directive, are clearly illegal, and
destructive of the relationship between citizens and their government.
The 1st Amendment also applies, in that free speech can also be private,
with unauthorized others excluded, for whatever reason, and/or
anonymous. If government intrudes, it has an unwarranted chilling effect.