But If I licensed the work under a free license They only can make the derivative work under the condition of releasing it under the same license. If they fail to do it they must talk to me and ask for a new license. Then I have the right to ask for a fair share of their profits. And it seems very reasonable that the share of the profits I ask must be higher than the cost of the activities I can't do because of they releasing the derivative work under a more restrictive license. If I copy back their derivative work and distribute it under a free license there is a loss of profits that can be measured by their fall of income. But they still may have some profits coming partially from their additional right and partially from mine. So I see the things this way Situation a) They use my work, do a derivative work and release it under free license: I copy their derivative work back to wikipedia and their ability to make profits is highly limited because of the existence of the copy in wikipedia and because of the free license they are releasing the work. Situation b) They use my work, do a derivative work and release it under a privative license. The free license doesn't apply because they don't accomplish with the conditions of the license. I can sue them and ask for a fair share of their incomes. No mater the original license because they are not using it. Here the problem is in supporting the cost of the legal process and being heard in a Chinese court. Situation c) They use my work, do a derivative work, release it under a privative license and I copy their work and distribute it under a free license. In this case They can claim for the loses of profits but they also have to compensate me for the fair share of their income I have the right to receive. I think is is not difficult to sustain that the second is higher than the first. And I also have the advantage that the case has to be heard in my country and if I don't have income or I am a none for profit entity accomplishing certain rules I have the right to free justice. I think situation is more difficult if I am not the author of the original work but only a distributor or a licensee. But if we could find a way to force any derivative work to enter under free license no mater what the author of the derivative work says then this would be the best protection for the free knowledge. If necessary changing again the license and explicitly saying: By using Wikipedia you are accepting that any copy or distribution or derivative work you may do will be also a free work. If you don't agree with this don't use Wikipedia and don't do any derivative work from it.