This isn't the way.
I know you are hurting and want to "hit 'em back." Me too. But there is no way you could successfully win a claim that GI controls a monopoly over the Stock Image industry. There are just too many other options out there. Sorry.
But here are some things we can do:
Choke them off: It almost goes without saying that we need to stop doing business with copyright trolls. And not just companies like GI, but their affiliates and subsidiaries. I have talked two clients out of sourcing images from iStockphoto because They are owned by Getty.
Education: If you belong to a user group or have a blog, I think it is important to get out honest information about what these stock companies are doing. There is a link on here that has someone from one of these stock agencies saying half of their income comes from PicScout. That indicates that HALF their income comes from these "extortion letters."
Help Matt: The top of every page has that Donate button. But even if you are broke, you can always volunteer to help out. Draft a letter to the EFF and post it and ask for feedback. Write a concise overview of the issue at hand and post it for comments. Use this to start contacting local media or blogs - like
http://www.chillingeffects.org.
I honestly think these actions will do much more to "correct" the industry than any accusations of monopoly.