[xorcist]

> you should prefer copyleft licenses over non-copyleft licenses,

For most, but not all, software. Stallman did famously argue for libvorbis, which you may know as the ogg codec used mostly by games and spotify, to be licensed under BSD instead of the (L)GPL.

[spauldo]

True, there are exceptions. Stallman thought strategically. Having a free-but-non-copyleft licensed reference implementation is necessary if you are trying to wrest dominance from an established but proprietary standard.

But I'm willing to bet that he'd have pushed for GPL if he wasn't trying to topple MP3.