That's not much of a defense at all, the cultural impact of Duke Nukem 3D is in the assets, not the code, though the BUILD engine was itself remarkable in its era.
Good on George for GPLing the engine, but his "openness to giving to the community" seems to stop short of anything that the mainstream public would benefit from.
And on a snarkier and less philosophical note: maybe Duke Nukem should be given over to the public domain. After DNF maybe someone else should have a shot. It, after all, would not stop Broussard from pursuing his own new Duke Nukem game, and might allow someone else to salvage a pretty influential part of 90s culture.
[edit] Thought about this some more. The return of a work into the public domain is less about the ability to redistribute it verbatim and more about the ability to extend and derive from it.
The cultural impact of public domain for Shakespeare are the million spinoffs, reimaginings, and new productions. The freedom to redistribute the original text is only a tiny part of the intent of public domain. This is the public good that comes from the work being in the public domain.
So GPLing the engine, or even opening up the assets, does not even begin to address the intent of public domain. Until someone (anyone!) can make a new Duke Nukem game, or a Duke Nukem movie, or a Duke Nukem novel (Prohibition-era Duke?), or incorporate Duke into some other work, the core intent of the public domain isn't being met.
> That doesn't sound like the grounds of creative control. That sounds like indefinite copyright absolutism.
Hm. Reading over the source (Facebook, not Twitter, but it's not substantially different as sentiments go), I agree. Perhaps I was being too generous with my interpretation.
Although he's against the idea of entering the public domain outright, he's not resistant to openness and giving to the community.