The freedom to study how the program works, and adapt it to your needs (freedom 1). Access to the source code is a precondition for this.
O RLY?
RMS got that part very very wrong. If the GPL was not about access to source but freedom to reverse-engineer, it could've become the ultimate viral license. Instead his harping on source code distracted the free software community from better RE tools and gave lawyers more to argue over. Access to
a general-purpose computer is the true precondition for this. He even wrote a story about this later (
https://www.gnu.org/philosophy/right-to-read.en.html ) but far too late. All the "walled garden" dystopian ecosystems are based on OSS, and sometimes the fat pigs in power even release pieces of it; but having access to the source does nothing. On the other hand, having access to the binary and a means to edit it is all you need.
Also, fuck those SJWs and their bullshite. They have a desire to destroy those in power because their retarded brains can't comprehend the thought of someone being more intelligent than they are.
https://dis.tinychan.org/read/prog/1525743384