In all this debate, one side of the issue never gets mentioned: why have legally sanctioned marriage at all? Is it really right for the government to dictate who can and can't marry eachother? Here's what I propose (and many libertarians share my opinion)
End government-regulated marriage. Allow any group of two (or more, see below for more commentary on this) consenting adults to enter into a legal partnership (which would have a neutral name and would NOT be called "marriage") by filling out a few papers. This would give them all the rights and responsibilities that marriage currently gives, and frankly, you can give most of those to another person who you're not married to by filling out papers anyway.
Then, allow for private marriage ceremonies. These could be religious (as in at a church or other house of worship) or secular. If the Catholic Church doesn't want to sanction same-sex marriage, don't force them to (as NYS would reportedly attempt to do). Gay couples can go to another church/religious entity, or opt for the secular route (see below).
Of course, interfaith couples, athiest couples, or anyone else who doesn't want to be married by a house of worship can opt for a secular route. This would be similar to getting married by a justice of the peace, except that the person performing the ceremony would not be licensed by the state. If the couple wants a mutual friend to officiate the ceremony, they can do so. The marriage ceremony itself would have no impact in the legal sense (as only the document I discussed above would create the legal partnership), so it wouldn't matter who performed it.
This way, the religious individuals who feel marriage should be between a man and a woman can join a church who feels the same way, get married in said church, and protect the sanctity of their marriage. However, gay couples would still be entitled to the rights and responsibilities of heterosexual couples, and would be able to get a full marriage ceremony, even if that ceremony had no legal impact. And keep in mind the marriage ceremony itself would have no legal consequence for ANY couples, so it doesn't constitute discrimination.
Above, I mentioned the quote "two OR MORE consenting adults". This is because some people believe in polygamy or polyandry. Most notably, many Mormons believe that a man should have multiple wives. In this case, the man in question could obtain a legal partnership (or whatever we're calling it) with all his wives, while taking into account that certain benefits can generally only be applied to one person. For example, complications might arise with regards to who would be given guardianship of children should the husband die. This could easily be resolved however, by the husband stating who would receive these rights when he fills out the necessary paperwork to create the partnership (or when the children are born, depending on circumstances).
This would also allow for more irregular marriages, such as group marriages or line marriages. I know many groups do not condone these unions and may even consider them immoral, but it is not the government's position to declare them universally wrong. Most religious bodies would likely choose not to sanction these marriages, and that of course is their right. But for those who do choose to engage in these partnerships, they may do so with full rights, responsibilities, and ceremonies presently offered by marriage.
People are debating about whether "marriage equality" must involve gay marriage. However, as a recent Libertarian Party release phrased it, "marriage equality [is] only one step towards ending legal discrimination." To quote the release:
"Marriage equality is not enough, .... I've heard some people express concern that allowing gay marriage would send us down a slippery slope. I hope it does. We should settle for nothing less than a society in which the legal code is wiped clean of references to a person's sexual identity or depends on how many sexual partners they have. It is disgraceful that we grant government officials the power to even examine such things, let alone criminalize any peaceful conduct between consenting adults or punish them with unequal marriage, adoption, tax, or immigration laws."
Therefore, we should outlaw any legal definition of marriage and simply allow any consenting adults to enter into a neutrally-named legal partnership.If they wish to have a private marriage ceremony performed for religious, personal, or any other reasons, they may certainly do so. And if people who don't support gay marriage wish to be married by an entity that also doesn't, they may do so and as such feel that their marriage sanctity has not been violated.
Now, for my opinion on how I would vote as an NYS Senator (as promised above): given the circumstances, I wholeheartedly would support the bill. However, I feel it is only an intermediate step towards truly ending discrimination. If you just skipped down here and don't get that reference, go back up and read the whole article.