It basically comes down to an ethical problem versus a moral problem.

The ethical issue is imposing our will upon others using our material in regards to material we did not create.  This is a relatively weak argument because the downstream user is free not to use our material with it's restrictive license.

The moral issue is, at core, the categorical imperative.  By applying our rights to our own standards we exert pressure towards compliance with our moral values, in this case expanding the commons. That weak preesure by control of our own works is a clear statement that we want everyone to act, wherever possible, in compliance with those standards and are demonstrating such by deed.

By way of noting the value of this license I note that a certain web site of recent and local controversy would be precluded from using works here licensed.   Had such licenses been in effect, understood and enforced by contributors there that controversy could not have happened.

I like it in terms of adding weight to expanding our values and propogating an understanding of them, but as said before I want to sleep on it.  Unless I think of something which I feel overweighs the moral value, I'll change my vote.