Paul: I believe the reason that the GNU libc was LGPL’ed (originally GPL with linking clause) was to allow X and several BSD applications run on the GNU system. Mainly because there was no point in starting a project that competed with XFree86 considering they shares most of the same goals of software freedom.
Stallman is always critical of the X licence. Stating that their licence does not defend freedom but instead tries to accomodate as many users as possible. From his point of view Free Software is primary, users are secondary as given all software users will gravitate towards Free Software.
The licence has had a nice (possibly unintentional) side-effect though. It’s made the GNU platform truly free. If you want to run propritery software on the GNU system you can. If you don’t want to, you don’t have to. It’s all about choice. Free Software gives it to you, whereas many propritery applications require you to sign strange licences to use their APIs.
I personally only run Free Software. Unless I’m teaching, then I don’t believe I should burden students with my personal preferences.