Is it "honorable" to fight an illegal war of agression?

Is it ethical to obey orders that further a war that violates countless aspects of international law, treaties and conventions to which the United States is a signatory? Because, under the US Constitution, those treaties and conventions are compelling legal authority to which all US citizens are bound, including those in the military. Orders in violation of those treaties and conventions are therefore *illegal* and thus the soldier receiving those orders has a DUTY to REFUSE to follow those orders.