How does the GPL help you gain access to the (trade secret, unpublished) source code for a proprietary application so you can fix a bug or enhance it?
By spotting that they've linked against or included GPL-licensed code, forcing them to stop distributing their binaries, re-write using GPL-free code, or release their own source code. Or, simply by setting an example and creating a community that they feel like contributing to and working with.
I don't propose to solve the issue of proprietary source, just that the Open Source/Free Software movement would still be known as the Public Domain movement if our laws weren't so screwed.
Sure, but by focussing on fair-use of binaries and eliminating copyright protection of GPL and similar licenses makes it possible for proprietary creators to incorporate GPLed code with impunity (which in turn will probably erode the community that developers Free software), whilst not enabling users of proprietary binaries to obtain the source for the applications they use and make use of them in the ways they wish. In other words, it'll make the current situation worse not better. Thankfully, PPUK leadership seem to understand this, these days, but it doesn't stop some of their supporters focussing solely on getting their warez without the risk of prosecution.