Marriage-equality proponents have finally had their day in front of the Supreme Court of the United States; we await a decision.
Before their decision, though, let's take a moment to examine why this is even an issue in the first place. It is a perhaps unfortunate situation that the word "marriage" is used for two entirely unrelated issues in the United States (and elsewhere): we use "marriage" for the religious commitment ceremony and also for the secular legal contract. Those arguing in favor of marriage equality are not attempting to somehow force the church to condone gay marriage; the church can believe whatever it wants, and given that the separation of the affairs of the church and the state is one of the principles this country was founded on, the opinion of the church should have no bearing here anyway. Rather, proponents of equality want simply for the government to be forced to treat heterosexual and homosexual unions equally, as guaranteed by the 14th Amendment to the Constitution.
That this is an issue at all is only because the government decided to get into the marriage business in the first place. By law, married couples enjoy all sorts of rights and benefits, such as tax benefits (the ability to file jointly, for example), medical benefits (a legal spouse is generally granted the power to make decisions given the incapacitation of the spouse), spouses not being compelled to testify against each other in court, and more. By refusing to view gay marriages as equal, all of these rights are denied to gay couples who wish to be married. Whether we turn to the 14th Amendment or simply to our own moral compass, this just isn't right.
There are two possible solutions: either affirm the right of gays to marry and have this marriage recognized in every state, with all of the benefits that entails, or completely eliminate the role of government in all marriage, returning the idea of marriage to a simple religious commitment. If we do not wish to be hypocrites in claiming America as one of the most free and equal places on the planet, these are the only options. Given these options, it is desirable to many, and frankly much easier, to take the first route.
Arguments that we should not be "redefining" marriage to "accommodate" the homosexual "lifestyle" fall flat. The church does not own the word marriage; allowing gays equality under federal law is not a redefinition of anything. Rather, for the first time in human history, science understands that homosexuality is not a choice, and more and more people are accepting this. I'd argue that all it takes is to ponder a simple question: whether you're straight or gay, is your attraction to a beautiful person automatic, or do you have to make a conscious decision every time you see one? If you answer the former, congratulations; you now understand why homosexuality is not a choice. It is, therefore, illogical to make any distinction in law between straight and gay relationships or marriages.
Religious people don't have to like it, but we do not govern this country based on religion. The equality movement takes exactly zero rights away from the religious; marriage equality does not affect a person's free practice of their religion, it does not harm the "institution of marriage", and it most certainly does not "destroy the fabric of morality of this country". It would be like a vegetarian claiming that other people eating meat in the same cafeteria as them somehow affects their ability to practice their choice of type of food to consume; the only difference is that one could make a logical argument that the smell of a delicious hamburger is tempting to a vegetarian, while marriage equality could not possibly tempt someone who isn't gay.
If you believe in the ideals on which the United States were founded, you must be for marriage equality. Love is love, and there is no rational reason to draw a distinction between heterosexuals and homosexuals on this issue.