A common argument against legalizing same-sex marriages is that doing so would undermine the institution of marriage. For some reason, a marriage between members of the same sex is a self-contradiction and, if their unions are legalized, then marriage itself across the country will be harmed. But upon what basis is such an argument made?
It certainly seems like an extraordinary claim how are we to make any sense out of the idea that a legal marriage between John and Frank could have any negative impact upon a legal marriage between Joe and Mary, much less undermine the marriage between Joe and Mary? What we must remember is that opponents of same-sex marriage are generally thinking less of legal marriage in the secular or civil sense and more of holy wedlock in the religious or sacred sense.
If marriage is a holy sacrament of a sacred religious institution, then it becomes easier to understand how a union that is regarded as an immoral abomination would cause problems. It would, after all, represent a form of desecration and that would be viewed as undermining a holy institution. Although these religious reasons allow us to make sense out of the claim, that doesnt mean that the argument is valid as has been explained elsewhere, the religious arguments against gay marriage are unacceptable in a society based upon secular laws.
Are there secular reasons for thinking that gay marriages might undermine the institution of marriage? If there are, they should be taken seriously. If societys goal is to support and encourage marriage, then naturally it shouldnt do anything that would only serve to harm marriage in the long run. Unfortunately for opponents of same-sex marriages, there dont appear to be valid secular reasons for thinking that allowing gay couples to marry will have any deleterious effects on marriage generally.
Some claim that it will undermine the idea that marriage exists for having and raising children a claim that seems far-fetched but which is addressed in more detail elsewhere. Others argue that gay people are less committed to monogamy than are straights; thus, gay marriages are more likely to be open marriages where the two people have a weaker commitment to one another sexually, psychologically, socially, and emotionally.
Such unions are perceived as weaker, but if the government validates them legally than others in society will be sent the message that such unions are just as valid as one where the commitment is strong. This undermines marriage because it undermines a central and essential facet of marriage: two people entering into a strong, committed relationship with one another. Society is therefore justified in not granting legal recognition to a class of relationships that will predictably be less faithful, less committed, and more fragile.
It is questionable whether the existence of open marriages harms marriage generally, and even more questionable whether there is some identifiable and quantifiable level of commitment that is necessary (and if there were such, wouldnt that mean that the government would have to start giving tests to all prospective couples in order to ensure that they rate high enough to be allowed to marry?). We can leave all of that aside, however, and accept those premises without also having to be persuaded of the conclusion that gay marriages are therefore undesirable.
For one thing, it is not clear those gay couples who already display the interest and willingness to go through the steps to come as close to marriage as they are currently allowed are in more open relationships than straight couples. Even if they were, they would not constitute a very large portion of marriages gays probably dont make up more than 10% of all people in society, so the number of open gay marriages would be far less than 10% of all marriages.
This doesnt seem like a large enough number to conclude that marriage would be harmed. If it were, and if that were a good enough reason to ban gay marriages, then we have a much better reason to ban divorce some 50% of all marriages end in divorce, after all, and it seems like an even stronger premise to say that allowing people to easily dissolve a marriage is ultimately bad for marriage as an institution. Funny, though, that the most vocal opponents of same-sex unions also arent campaigning in defense of marriage by trying to ban divorces.
Although there do not appear to be any secular reasons for prohibiting members of the same sex from marrying, this sort of argument is probably the only one which opponents of gay marriages can realistically expect to use if they want to make a legal and moral case. They need to provide some evidence of clear and identifiable harm that would result from same-sex marriage. In other words, they need to be able to demonstrate that the harm will outweigh any benefits.