Regarding the legal risk of violating GFDL (and thereby someone's copyright) on en. Wikipedia:
American Wikipedians are reasonably safe, I suppose. I am not sure about non-American en. Wikipedians, since that may entail implications on international jurisdiction and choice of law.
Whenever we speak of legal risks associated with GFDL, we have to face the issue that at least in English Wikipedia, there seems to be no official, agreeed-upon interpretation of the GFDL (what is "work"? who are the copyright holders? are images under GFDL? is Page history the history as in GFDL? etc.)
But that aside, here are the defenses that I find quite significant:
1) We only need substantial, reasonable compliance rather than a strict, literal compliance. (http://mail.wikipedia.org/pipermail/wikilegal-l/2003-November/000084.html and http://en.wikipedia.org/w/wiki.phtml?title=User:Michael_Snow/Candidate_state...)
2) One has to register his copyright work. Unless otherwise, he may not be able to sue the violator in a Federal Court.
(http://meta.wikipedia.org/w/wiki.phtml?title=Do_fair_use_images_violate_the_... * and http://mail.wikipedia.org/pipermail/wikilegal-l/2004-February/000261.html)
* A sidenote - Although Alex's remark there is a bit agressive, the matter is now solved between the involved parties, as I understand.
3) Coauthors of a work cannot sue each other regarding copyright violation. (http://mail.wikipedia.org/pipermail/wikilegal-l/2004-February/000261.html)
4) The moral rights are not protected under the U.S. copyright law much, so that even if a lawsuit is brought up, there won't be much of a damage to be found. (http://mail.wikipedia.org/pipermail/wikipedia-l/2004-February/014275.html)
5) In addition, if Terms of Use becomes effective sometime in the future, as proposed in the expanded version, it may prevent any lawsuit between two Wikipedians. See the arbitration clause in the following page:
http://en.wikipedia.org/wiki/Wikipedia:Terms_of_use_(proposal)
All combined, it seems that current practice is reasonably safe for American Wikipedians. Yet it seems quite possible, for example, a troll registers a work and tries to sue someone who strip attribution from his contribution by moving it to meta or a talk page from village pump.
Also, some features of the U.S. courts are said to be riskier or a bit unpredictable in comparison to Japanese courts. (See: http://article.gmane.org/gmane.org.wikimedia.legal/263)
And last, but not the least, I am not sure if it is okay to just say that we should keep violating GFDL just because it cannot be held accountable in court.
So again, it is better to have something like the PD license in palce even from at this point, I am inclined to think.
(Disclaimer: I am not a lawyer. And the citations I provided above are not legal opinions, either.)
Best,
Tomos
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