Another of the most common arguments for gay marriage deals with religious grounding on the part of many people who hold to the current definition of marriage being between one man and one woman. It is argued that because of its religious nature, the definition of marriage needs to be revised. It needs to be more secular in order to not force religion on anyone.
The main problem with this argument, besides misunderstanding the nature of the separation of church and state, is that if you remove a religious basis for ethics and replace it with a secular one, you end up with a relativistic ethic. In a secular ethic there is no place to ground morality. Whether you ground them in the individual, a community, or some pragmatic end to which the ethic should be a means, individuals and communities tend to disagree. They also disagree with which pragmatic ends should be sought. In the end a secular ethic becomes self-refuting leaving no actual grounds to say that the current definition of marriage is wrong. This type of ethic always boils down to power because there is no real right and wrong. If the group who wants to promote gay marriage has more power they will win, or vise versa. But if this is the case, it would be illogical to say that it is unethical to not allow homosexuals to marry. Instead the argument should be, “there is no real right and wrong, and we desire gay marriage and we are tying to see if we have more power than those who don’t.” All appeals to equality, or separation would be mere smokescreens masking a play for power.
Finally, if someone does want to appeal to a universal transcendent objective ethic, there is no way to escape its religious nature, and in the end this would refute the separation of church and state argument stated at the outset.