Kevin, all your argument allegedly proves is that if "ought" is to be derived from anything, it must be derived from an "is" rather than an "is-not" (whatever that means). Your argument doesn't even attempt to show that "ought" CAN be derived from "is", and simply assumes that an objective "ought" must be derivable from something. That's a clearcut instantiation of the http://en.wikipedia.org/wiki/Naturalistic_fallacy.
It's a very bad sign that the term "naturalistic fallacy" shows up nowhere on aynrand.org. A search for "is-ought" there only finds a videotape by "Harry Binswanger" called "Bridging the Is-Ought Gap", with no hint how to get it. Searching the whole web for these terms with the conjunction "by Leonard Peikoff" turns up nothing edifying, either.
For a group that claims to have solved a centuries-old fundamental problem in ethical philosophy, these Objectivists sure seem shy about explaining how they did it. If the Objectivists aren't going to take mainstream philosophy seriously enough to engage its standard literature and terminology, I don't see why anyone in the mainstream should bother engaging Objectivism.
