In a nutshell, the argument works from the premise that there's a right to due process, which includes the right to a hearing. By analogy, Harel argues that there's a process value in constitutionalism and judicial review. Just as it's good to give people a chance to be heard even if the hearing doesn't alter the outcome, it's better for rights to be enforced as a matter of duty - by constitutionalism and judicial mandate - even if the legislature might have done the same thing anyway. I found this argument fascinating, and thought-provoking, especially because it proceeds on such different lines than American debates about judicial review and constitutionalism normally do.