High-quality crypto libraries / systems lead to broader implementation, which makes it harder for elements in mostly-free societies to pressure implementers.

It's one thing for the NSA to quietly lean on ATT (and only ATT). It's a completely different thing for them to quietly lean on 1,000 different organizations and authors.

Similarly, it's easy to sneak a CALEA-alike amendment into national law when only PGP exists. It's harder when the narrative becomes "The government wants to take {beloved product used by millions} away."