- http://commons.wikimedia.org/wiki/User:Gmaxwell/An_alternative_model_for_license_compatibility (alternative)
My reasons for deciding not to use the CC-By-Sa licenses are fairly long and complicated. I don't have the time right now to really dive into it as I'm rather busy. For the purpose of the Foundation's announcement it was enough to say that I have explicitly rejected those terms.
Your question is interesting and deserves a response. So I will provide some quick examples now, but by no means is this my complete position on the reasons I have decided to not use those licenses for my work.
1) Laurence Lessig has posted multiple times claiming that it is acceptable to take illustrations licensed under CC-By-SA and produce combined works which are not freely licensed. For example, if I wrote a since instruction book and created illustrations on how to safely use a bunsen burner a commercial textbook publisher could use my illustrations in their textbook without giving anything back the the world of free content.
I use a copyleft license for my content because copyleft licenses create an incentive to release works under a free license. I see this both as the 'payment' for my works and a way of ensuring that my contribution stays free and isn't captured for the sole profit of another party. With my works copylefted someone creating a new work could choose to purchase commercial stock photography, or they could choose to freely license their work and build off mine.
When someone is really unwilling or unable to freely license their derivative I am willing to license my rates under typical commercial stock photography rates. This provides me with, well, lets just say that I make enough doing this that I report it to the IRS.
Some people are happy with using very liberal licenses (e.g. releasing their work as 'public domain') for all their work and I support their decision, but I've seen first hand how the small friction of copyleft increases the pool of content that is freely available for all, and I wouldn't want to lose that for my illustrations. (For my own works of trivial merit, I 'PD' them because I don't expect any copyleft gains)
Mr. Lessig's position on "share alike" and illustrations isn't well supported by the text of the license, but his position naturally carries a lot of weight.
- And this has exactly been our interpretation of the GFDL -- this is why we permit combining GFDL works with media under any license whatsoever (limited only by policy), because we regard the media and the text to be "separate and independent" as per the GFDL.
- I believe what is needed is a new, strong copyleft license for "embedded media", which is unambiguously explicit about the consequences of embedding a photo into an article, or a sound clip into a video. I've already talked about this with Larry and other CC folks, and would be happy to see you join these conversations.
- In my opinion, this interpretation is inconsistent with the text of the GFDL. When the text of an article or other document relies upon a GFDL image to communicate part of its message to the reader, in my opinion, that text can not realisitcally be considered "seperate and independent" of the image. I do not believe embedding GFDL images in non-copyleft documents can be considered consistent with either the text or the spirit of the GFDL.
- Personally, I take this issue quite seriously. For example, I reached an out-of-court settlement with a major publisher who took images I had included in Wikipedia under the GFDL and used them commercially without honoring the copyleft provisions.
Greg will of course correct me if I'm wrong - but I suspect the problem is that lots of people want CC-by-sa because it's easier to reuse stuff ... but that GFDL makes it hard to reuse stuff is considered a *feature* by many, e.g. photographers who license work as GFDL but also sell it privately. That is: the thing that makes GFDL a pain in the backside for a wiki is precisely why they like it, and they want it to stay a pain in the backside for that reason.
- I don't know of anyone who doesn't want their photographs being used in freely licensed work. The contention on this point is that the creative commons cc-by-sa, per the position pushed by the creative commons allows people to make non-free works out of cc-by-sa images. There are people, myself included, that think this defeats the purpose of free licensing in this context.
- Let's make a strong copyleft license that appeals to photographers.
- Ah, yes, the GFDL as "CC-BY-SA online and no-one dares use it offline"... I certainly understand that appeal
- It's worse than that - I suspect that's been advocated as a feature to more than a few photographers to get them to put stuff onto Commons for our use. I don't *think* I've used it that way myself, but I'm currently wracking my brain trying to think of anyone who I might have. These people *will* feel ripped off.
- We could, for a transitional phase, allow photographers to change license templates on media they hold the copyright to from a (arguably or not) permissive copyleft license, to an explicitly strong copyleft license. This would not invalidate the old templates, but at least ensure that people finding the files on our site would be asked to respect the strong copyleft provision. After the transitional phase, strong copyleft would just be a choice for new uploads. This all presumes the existence of a strong copyleft license in the first place. :-)
Misleading front cover text 
2) The Creative Commons licenses come with misleading front cover text. If I released my work under these licenses I would be at constant risk of suffering disputes resulting from reusers misunderstanding their rights and obligations. We've experienced the reverse of that numerous times at Wikimedia when people using CC-By-* expect to be able to exactly stipulate how attribution is provided.
- This is easy to fix. Do you have a document that enumerates thechanges you'd like to see made?
Attribution to service provider 
3) Speaking of 'attribution', the Creative Commons cc-by and by-sa licenses at version 2.5 and beyond contain a serious issue with their attribution. The attribution clauses in these licenses reads, in part,
"If you distribute, publicly display, publicly perform, or publicly digitally perform the Work or any Derivative Works or Collective Works, You must (...) provide, reasonable to the medium or means You are utilizing: (i) the name of the Original Author (...), and/or (ii) if the Original Author and/or Licensor designate another party or parties" (...) (through) terms of service or by other reasonable means"
So these by-attribution licenses don't actually provide attribution if a service provider specifies so in their terms of service. Jamesday (en User:Jamesday), a Wikimedian old-schooler, wrote a lot about this back when these terms came out.
Obviously the issue of attribution for collective works in a space limited medium is important, but it can be addressed without giving service providers the ability to take attribution for all freely licensed content distributed through their systems.
The exact implications of that text aren't entirely clear: If the clause only takes effect at the first point of submission it breaks the right to fork, and fails to resolve the collective attribution problem (i.e. you end up with "This article contains material by Wikia(tm), WikiHow(tm), Wikipedia(tm), GregPedia, Planet Math ..."). Or, alternatively, if any down stream service provider can invoke it .. it allows anyone who could claim to be a service provider to remove attribution at any time... which many consider to be morally offensive, and which present practical problems for people trying to keep works free.
Years ago when these terms were first released I was seriously concerned with the implications of giving an author's service provider a special rights in free content licenses. In these days of real concern over net-neutrality my worries on these matter are even greater.
And from here, we could go into the issues with the Creative Commons branding, which many people feel is exploitative, and which Creates Confusion with respect to the licenses. ... which is a matter of great concern to anyone who thinks Free Content should be more than CC-NC-ND.... but I've run out of time.
- As far as I can tell it's pretty clear: The copyright holder determines whether or not they want to designate someone else for the purpose of attribution -- and a participatory website like a wiki can _require_ such designation. Wikinews actually does: On the edit screen, it states that you agree that your edits will be attributed "to Wikinews".
- Correct me if I'm wrong, but I believe Creative Commons added this option specifically to _help_ wiki communities in making attribution more manageable. They originally wanted to create a CC-WIKI license for this purpose, but instead modified their existing licenses to be more flexible.
- It seems to me that CC has a history of addressing stakeholder needs. If we were to adopt one of their licenses, we would instantly become one of the most significant, if not the most significant, stakeholders -- and I do believe our concerns would be taken very seriously, as I think they already are.