There is a difference, in public discourse, between what is true and what is civil, or what equality thinks appropriate. The issue here is about how the Christian participates in the State.
We noted above that the main function of public deliberation is not to prove that one’s views about the public good are true, but rather to show one’s fellow citizens that one’s views about the public good are justifiable. And to show one’s fellow citizens that one’s views about the public good are justifiable is to show that they are justifiable to them. In order to show that one’s views about the public good are justifiable to your fellow citizens, one must articulate the case for one’s views in terms that do not presuppose one’s own particular moral, metaphysical, or religious commitments. For your fellow citizen may reject these commitments without thereby disqualifying themselves for democratic citizenship.
An example will help. Imagine a fellow citizen affirming that the state ought to prohibit same-sex marriage because God forbids homosexuality. Here, what has been offered is a reason that could count as a reason only for those who hold certain religious convictions. But free and equal citizens of a democratic society are not required to have any religious convictions at all. So the justification proposed fails to show that the position is justifiable. Contrast this with the case of a fellow citizen who affirms that that the state ought to prohibit same-sex marriage because permitting it would weaken the stability of the family, thereby weakening the most basic institution of all human society. Social stability is a concern for democratic citizens as such. Accordingly, in response, a critic will challenge the claim that allowing same-sex marriage will undermine the stability of the family, and thus social stability overall. But the important thing is that the social stability argument proposes a reason of the right kind. Those who support same-sex marriage cannot simply say in response, “Who cares about social stability?” They instead need to engage with the reasons offered by the same-sex marriage opponent. To be sure, we are confident that the social stability argument against same-sex marriage falls short, but that is a different matter from what is now at issue, namely, which reasons are properly public.
We may say that public reasons are of the kind that cannot be dismissed as irrelevant or unintelligible by democratic citizens. Thus there is a fundamental difference between a reason such as “The Bible forbids it” and “Equality requires it.” One who dismisses the former does not thereby disqualify himself for democratic citizenship; one who dismisses the latter does. Accordingly, a group of citizens that insists on a public policy that can be supported only by means of nonpublic reasons thereby shows disrespect for their fellow citizens. Put otherwise, to affirm a public policy that cannot be supported by public reasons is in effect to say to one’s fellow citizens “Because I said so.” And that’s to deny that one’s fellow citizens are one’s equals. That’s disrespectful.
Indeed, it’s uncivil.