The FARs say that class D is controlled airspace. They also say that you
have to obey ATC instructions. What are the tower controllers controlling
there if not air traffic?

They are not controlling air traffic in the sense of taking
responsibility for separation (which they do in IFR for example, and
perhaps in positive control areas - a controller will certainly jump
in and clarify)

That they can keep you out is true, but not relevant to my point (of
it being primarily a pilot's responsibility to see and avoid)

Jose
--
Freedom. It seemed like a good idea at the time.
for Email, make the obvious change in the address.