Marriage being between man and a woman isn't a value. The value is that family is sacred and marriage commitments are important; heterosexual marriage is the traditional way in which that value has been represented. (For the record, though it's been said a thousand times before, it bears repeating: What we now consider "traditional" marriage is already not what traditional marriage used to be, and it is universally agreed that that is an excellent thing. So let's maybe acknowledge that "tradition" isn't the best argument in the arsenal where marriage is concerned.) Same-sex marriage is based on exactly the same thing as heterosexual marriage: love.
Judging homosexuality as a sin isn't a value, either. It's tradition, all right, but Jesus didn't do it and he didn't teach it. In fact, the value he did teach was pretty much the opposite: that we shouldn't judge the woman "taken in adultery", that we should love and care for people as we would treat Jesus himself, and—this was apparently important—that we should not judge others. The value people seem to think they're living is "standing up for their beliefs," but I don't actually remember Jesus making that a really high priority. Basically, we feel that it's more important to make sure everyone knows we follow Jesus—which Jesus kind of counseled against—than it is to actually do what Jesus told us to do.
Let's address the "right to life" argument that's generally considered a traditional value. The actual value behind this belief is that human life is sacred. The behavior—the politicized belief that government should restrict abortion—that is not a value. That behavior disregards the life of the woman involved; it doesn't respect all life in the equation, just the one that's politically important. It takes away a woman's agency (which is pretty damn sacred to Mormons, at least, if not to other Christian denominations). It has good intentions at heart, but it's founded on misapprehensions (oh so many misapprehensions)—the belief that women who get abortions are motivated by selfishness or carelessness, the belief that a child's life is a consequence a woman must accept for having had sex, the belief that ending a pregnancy is the same as murder, the belief that other people have the right to control a woman's body and reproduction. Banning abortion is nothing more than a patriarchal society's way of exerting control over women and preventing them from having power over their own lives. Banning abortion actually does not cause fewer abortions; it just causes more women to die. This is absolutely a lose-lose situation if you think life is sacred, so if that were really the motivation behind the political movement, the movement would have ended when that information was discovered. But that's not what the movement's about; it's about controlling women. The political behavior associated with the value is not actually the value itself.
Something to consider:
The worst sinners, according to Jesus, are not the harlots and publicans, but the religious leaders with their insistence on proper dress and grooming, their careful observance of all the rules, their precious concern for status symbols, their strict legality, their pious patriotism.
—Hugh Nibley, "What is Zion? A Distant View," Approaching Zion