The Ask.com web site has an article on philatelic literature – Philatelic Information and Knowledge: Pass It on by John Finch which publicizes the American Philatelic Research Library (APRL).
The free exchange of information in the philatelic world is free only insofar as one may not have to make an expenditure for specific knowledge. That is, one can take advantage of fine philatelic libraries owned by the American Philatelic Society, but only after membership dues is paid. No one would question this. And the amount of information available to one for the price paid for all the organization’s benefits makes the dues a bargain.