“Crucial to the resolution of this case is the fundamental social justice principle that those who have less in life should have more in law. The party-list system is one such tool intended to benefit those who have less in life. It gives the great masses of our people genuine hope and genuine power. It is a message to the destitute and the prejudiced, and even to those in the underground, that change is possible. It is an invitation for them to come out of their limbo and seize the opportunity."