With free software you also give potentially bad people access to your work. I would hate to write something and then find out that it's being used for evil. Proprietary software isn't necessarily harmful and free software isn't necessarily good. Also, how is MIT and BSD compatible with GPL? I thought they weren't copylefted.
On the proprietary side you have Microsoft, Apple, and Google. On the free side you have Stallman and his zealots. There's not much in between.