I think many creators of GPL software see it differently, and wouldn't be ok with people making proprietary modifications to their code, even if anyone was free to disassemble the modified code and try to make sense of it.
I know many creators of GPL software would absolutely see it differently, but they still wouldn't get to tell me how to use my own computer. Restrictions on your freedom to express yourself is what the GPL was designed to fix, even though it itself is a restriction on your freedoms.
