> Preventing someone downstream from adding constraints is, in itself, adding a constraint.
Yes, it is. As in one (1).
> The argument you make about other possible actions also applies to the-action-of-closing-the-thing-off
Uh? How many actions are made possible by a company closing access to a version of a free project? Even if this closing-the-thing-off creates some possibilities, those will be limited to the company that keeps the version to themselves. How can the amount of these actions be larger than those actions available to all the other people, who are now unable to use that version?
> I'm just pointing out that what we've got here is a group that is arguing in favor of restrictions of a certain type because they say that restrictions are, in themselves, wrong.
This is not how I see it, and I'm an advocate of Free Software (including and preferring the GPL share-alike version), so you may be attacking a straw man there. In fact, I'd say that the people defending BSD-like licenses are more prone to making the "restrictions are wrong" argument.
> I wish that people who zealously supported GPL-style licenses would acknowledge that they are taking away a certain set of otherwise-available rights concerning what others are allowed to do with their software - NOT maximizing possibilities, but instead restricting them to a certain set they find agreeable.
I do acknowledge that share-alike is restricting some actions that are possible with BSD-like, but overall I believe that this constraint DOES maximize possibilities when seeing the big picture.
As I've argued above, the idea of those constraints is that the constrained environment should have more total possible actions in the aggregate, even if every individual player has one less action available on paper. If you don't acknowledge this possibility, you are not getting the point why the constraint was added to this kind of license.