What religious values should the state take into account when sanctioning marriage? Well, perhaps we should first ask what religious values the state currently, right now, takes into account when sanctioning marriage. I can't think of any uniquely religious values that are involved in typical marriage licenses. When I look at the various reasons a state uses when denying a marriage license (the people are already married, for example), I see nothing religious in the reasons.
Just about anyone can get married for just about any reason — including a drunken whim — and few if any are actively protested and opposed by the Christian Right. I see nothing inherently religious in the state sanction of marriage generally or any marriages in particular. There is certainly nothing especially Christian or biblical about civil marriages in America, as demonstrated by the fact that atheists, Hindus, Buddhists, Jews, and every other non-Christian can get married without being questioned about it.
Christian conservatives who are most vocal in their opposition to gay marriage also make the argument, implicitly or explicitly, that their religious values should be incorporated into the state sanctioning of marriages. This would represent a significant change from the current situation which no conservative Christians are prepared to explain or justify. Religious values aren't incorporated into state marriage licenses today, so why should we start tomorrow or next month?
Furthermore, whose religious values should be incorporated into civil marriages? Christian? Muslim? Buddhist? Picking one religion over others, and mostly likely one segment of that religion over all others, would be unavoidable. Why Catholic Christianity over Lutheran? Why conservative evangelical over Unitarian Universalist? There's no way to make such a choice legitimately — civil marriages exist for all citizens, regardless of religion or religious beliefs. The "religious values" of one religion, denomination, or religious group cannot be incorporated into state definitions of marriage without shattering the separation of church and state.