StackExchange is not the owner of my contributions and is not allowed to change the license without consent/permission.
Who owns the rights?
If the publisher, ....
- A couple of options for obtaining permission to relicense:
- upon upload by contributors, have a prompt box to obtain agreement to relicense previous uploads;
- general outreach to contributors seeking agreement to upgrade. [Note that this is easier to do with discrete artifacts (an article, a photo) as opposed to other contributions such as comments on wikis and similar, where one person's contribution is intermixed with others.]
Stack Exchange does not own the rights and did not follow any path to obtain permission to relicense. Thus they do not comply with the true license and neither do they respect the contributors.
So how do I get my content either reverted to 3.0 or how do I get it removed?
How do I get support in this cause? (e.g. collect a large group of people that want to do the same, signatures, lawsuit, etc.)
Some people have noted that there may have been no violation of the law, and there is a relation with section 4.b that allows re-licensing (within certain bounds) of adapted works. However section 4.a clearly states that
4.a You may Distribute or Publicly Perform the Work only under the terms of this License. You must include a copy of, or the Uniform Resource Identifier (URI) for, this License with every copy of the Work You Distribute or Publicly Perform. You may not offer or impose any terms on the Work that restrict the terms of this License or the ability of the recipient of the Work to exercise the rights granted to that recipient under the terms of the License. You may not sublicense the Work. You must keep intact all notices that refer to this License and to the disclaimer of warranties with every copy of the Work You Distribute or Publicly Perform. When You Distribute or Publicly Perform the Work, You may not impose any effective technological measures on the Work that restrict the ability of a recipient of the Work from You to exercise the rights granted to that recipient under the terms of the License. This Section 4(a) applies to the Work as incorporated in a Collection, but this does not require the Collection apart from the Work itself to be made subject to the terms of this License.
So this seems very clear (section 4a applies to the works and not 4b). StackExchange can re-license their collection according to the terms in 4b, but for the individual works they need to comply with the terms in 4a and they should keep the license 3.0 for the individual works.
(e.g. they could place next to all posts small links that refer to the specific license(s) that apply for those works, it doesn't need to be great; they could ask people to give permission for 4.0 and then remove those links for the specific posts and make the footer text something like 'user contributions licensed under CC BY-SA 4.0 with attribution required. Unless otherwise stated' or in some other way. It is a big pain to deal with this mixed license material; but we should respect the rights of the contributors and not just change licenses in the way we like and without permission. Make something of your own if you do not like it).