I hope to bring some clarity to the language of rights used of gay marriage:
Constitutional amendments defining marriage as a (monogamous) union between one man and one woman only, whether you think them silly or not, do not prevent same-sex couples from going to some kind of institution that considers same-sex marriages to be valid and get a ceremony.
The state refraining from legally recognizing marriage between two persons of the same sex is not about punishment or the harm principle. If we’re going for neutrality, neutrality is the government refraining from making any legislation related to marriage. As it is, government recognition of marriage between two persons of opposite sexes is a notional subsidy – in the form of a blessing of sorts – for what it (ostensibly) recognizes as a positive externality and thus a collective good for society. Non-recognition of homosexual relationships as marriages, then, has nothing to do with punishment, much less with punishing anyone for having sex with someone of the same sex.
If you want to push for the state to treat same-sex marriage exactly the same as it treats opposite-sex marriage, you have two choices. One is to make a case that marriage between two persons of the same sex produces a set of positive externalities that warrants the same levels of subsidy as are accorded to opposite-sex marriage: this, if convincing, leads to a prescription for recognizing same-sex marriage. The other is to make a case that marriage between two persons of the opposite sex does not produce any set of positive externalities that warrants public subsidy: this leads to a prescription for the repeal of any laws dealing with marriage at all.
If it’s not about marriage, of course, make laws that are not about marriage to begin with and thus avoid the matter entirely – as perhaps it should be. Religious institutions and other associations in civil society remain free to bless or disapprove of unions as they see fit, regardless of how the government treats each. This is a liberty right, then, not a claim right: that the government must let you go to some organization to get some ceremony done and then let you call it a marriage, as long as you don’t make the government call it a marriage too.
So attack such measures, such as Prop 8, as silly legislation, not as an infringement on the “right to marriage”. How is recognition of what you call a marriage a right, whether that union is with the opposite sex or with the same sex, if the temporal authority decides to stop dealing with it at all as a legal category?