There are abundant resources available online in NTRS about the hard earned knowledge of rocket science. But NASA makes them available for free for all.
But there does exist some classified documents. So, on what basis does NASA decide to release its work to public?
Considering the argument that NASA functions on tax payer's money, and hence releasing to public is essential only raises another question - why make it available to the entire world?
There are other government organisations that simply doesn't release much information, compared to NASA. There must be a compelling reason for NASA to do so and to continue the policy.