[swatow]

You are giving the FSF point of view, but that is not the only point of view. The post is correct that the practical effect of the GPL is to require giving back to the community.

Freedom is a loaded word, and I think most people don't share the FSF's definition of freedom. I would rephrase your statement as "the GPL is designed to globally maximise the ability to use, modify and distribute a piece of software. The only ability the GPL does not provide is the ability to take these abilities from future uses."

I personally think that this ability to modify software (and scrutinize its source code) is very important when it comes to the operating system. For javascript code sandboxed in the browser, it is much less important (sure, javascript can still do unexpected things, like tracking users, but this is still much much less than what could be done with full user level access, and these are things that can be fixed). So I support GPL for operating systems, encourage open source for other software, but don't object to closed source when the danger is low.

[TuringTest]

  "the GPL is designed to globally maximise the ability to
  use, modify and distribute a piece of software. The only 
  ability the GPL does not provide is the ability to take 
  these abilities from future uses."

I would summarize that as "the GPL is designed to globally maximize knowledge about the software, and the ability to use that knowledge".

The part about forcing published forks to release their source code is a consequence of that purpose: hiding the source would reduce the amount of knowledge, and thus it is forbidden.