Not affording the Convention's protections to those that do not qualify sends the signal that we are following the Conventions! It sends the signal to our enemies that no matter what they do in violation of international law that they will be insulated from the consequences of those violations.
And in a war where the Geneva Conventions are never followed by our enemies, why are we worried about defining the terms of the Conventions more precisely? This is the sin of the Bush Administration and most Republicans in Congress.
By agreeing to even apply the Conventions to those undeserving of their protections, both sides agree to an entitlement for terrorists. What is now being argued are only the terms of that entitlement.