"If the program dynamically links the plug-in [...] they form a single program, which must be treated as an extension of both the main program and the plugin.".
To understand just how nonsensical this position is, let's flip things around a bit: You distrubute a program you wrote, let's call it coolprog. It's free, but released under a proprietary license that allows arbitrary redistrubition.
A year later, I begin work on implementing a glibc replacement completely from scratch. I code furiously for a weekend, fueled by copious amounts of Shasta and an all-Rush mixtape, and finally release my new masterpience: an ABI compatible glibc replacement. I license it to the world under the GPL. Next, I download a copy of your program, package it up with a copy of my library and a script to launch it, and release it. Per your license, this is perfectly fine: after all, you allow redistribution.
Except, one of the things my script does is to use LD_PRELOAD to force-load my glibc-replacement, which, if you will remember, I have released under GPL, instead of the standard LGPL version. One person downloads my release and proceeds to run it. Your program now gets dynamically linked with my GPL'd glibc replacement. And now what?
Under the "if the program dynamically links the plug-in [...] they form a single program, which must be treated as an extension of both the main program and the plugin." interpretation of the FSF, your program has linked against my GPL work and, therefore, is a derived work... Right?
This is just one small example of why the "linking creates a new derived work" notion is bullshit..