You don't actually need to sue people to make GPL have an effect. Some companies might casually infringe copyright, but they are less likely to do so once informed about it by the public. At that point, it becomes willingly infringement. Willingly infringement on a commercial scale is one of those key legal terms that turn fines into millions, and in some countries, can even become a criminal offence rather than civil (criminal offences are handled by the state rather than by the complaint).

This is true in theory, but in my experience, every big company asks for all the licenses of the software they use, and if it's GPL, that's a non-starter. Maybe I've only worked for the good ones.

Obviously there will be some that violate the license, as there is with any license. But the point is that you do have _some_ sort of legal recourse if they do, and also, you make your intent clear as an author: this is supposed to be Free forever.

If your anti-argument is "people will just ignore the license," then using a permissive license isn't an argument either. After all, people will just ignore it.

It may be a cultural difference. As I recall, Landley's examples are from the East (Sony, for example). Intellectual property as a sacred institution is somewhat less established there than in the West.

The point is that users who would give credit will do so anyway (without needing a gun held to their heads), and those who won't, won't. A license only changes things by giving the recourse to sue in the latter case. If you aren't going to sue anyway (as Landley isn't, anymore), then there's not much point to using a relatively restrictive license.

I recommend watching the Landley talk. He used to be among the most rabid copyleft advocates, before the BusyBox fiasco and GPLv3.