It's not worth my time to find out who is behind the letter. It hasn't been picked up anywhere except here, from what I can see.
What's more depressing is that so many people here have been aghast at certain names, proclaiming, Oh I thought better of them!
Well, think better of them, then! Question whether they would put their names to a letter like this, if everything you know about them thus far suggests that they wouldn't. I despair at the lack of critical thinking on both sides of this topic, I really do.
To be honest, the most hurtful thing I have read on this thread has been the person who said there weren't any "big hitters" on the list. OUCH. ;)