The argument presupposes that we are somehow aware of some sort of perfect moral standard at this point in time and that the only thing left to do is to impleme

The argument presupposes that we are somehow aware of some sort of perfect moral standard at this point in time and that the only thing left to do is to implement it to all of society through the method you describe. In the era where they saw disease as a divine punishment, most people no doubt held this belief as well. In reality, moral standards will shift around as they always do, some parts will lose their luster and others will be strengthened. New standards will emerge and make our current progressive ideals seem distant and alien, the same way we look at medieval ostracism.