Why you should join the FSF ? That's simple, the FSF is a consistent organization. Just take a look at this GNU's Bulletin published in 1987. They were already fighting against DRM (before named like that).
Just when science is making it possible to copy music perfectly, record companies are trying to make it impossible again, with government-enforced copy protection.
Looking in the past, the first GNU's Bulletin shows an interesting historical part :
Schools will be able to provide a much more educational environment by encouraging all students to study and improve the system code. Harvard's computer lab used to have the policy that no program could be installed on the system if its sources were not on public display, and upheld it by actually refusing to install certain programs. I was very much inspired by this.
I'm just now wondering what's the current policy at the computer lab at Harvard. It could be highly symbolic to go at the today Harvard computer lab and check with them if they can show all the sources for the installed software on their system. FSF is still ahead and it's still the right time to join them. We need freedom in today's world and free software is playing a pillar role as the shift to an information society is a reality.