Astronomical telescopes are not optimized for Earth surveillance tracking and targeting, and this one will be orbiting out at the 2nd Lagrangian point, too far from Earth to do much good for espionage. It is also set up for observing in the infrared, it specializes in mapping cold gas clouds in deep space, not objects on our planet. I can't think of any potential reconnaissance or IMINT application for this bird that couldn't be carried out much better and cheaper by some dedicated spook platform. This is also an international project, other nation's space programs and the ESA are involved. All this suggests there is no need for security here.

Observing times on space telescopes are competitive and have to be scheduled and approved months in advance, and extensively rehearsed. Kicking a science user off-line unexpectedly to do some intel work would give the whole show away, not to mention that the data telemetered back to earth is non-encrypted, and vulnerable to eavesdropping.

All I can think of, and I am totally speculating here, is that some of the technologies aboard this spacecraft are classified, or that the US does not want to add to the tiny pool of people in the world who can do this sort of work without making sure they're on our side. It might give away too much about our intelligence gathering capabilities.

Or maybe, just maybe, they really expect to find something "out there" they want to keep us in the dark about as long as possible.