One of the arguments (which isn’t really an argument) that proponents of “same-sex marriage” put forth is an emotional appeal that follows along the lines of: “So, you don’t support marriage equality for homosexuals; I bet you would have opposed the repeal of the miscegenation laws, that prevented mixed-race couples from marrying”. The assertion is usually some variation of that statement.
It is an invalid comparison, however, because the situation is different. With the miscegenation laws, a white man could marry a white woman, but a black man could not marry a white woman. In the same way, a black man could marry a black woman, but a white man could not marry a black woman. The white man was granted a privelege by the government that the government then denied to the black man, and vice versa.
With regard to same-sex marriage, heterosexuals do not have a right to marry someone of the same sex that is then denied to homosexuals. However, homosexuals are not prohibited from marrying someone of the opposite sex. The situation we have at present is “marriage equality”.
What the proponents of same-sex marriage wish for is an expansion of the definition of marriage to include same-sex couples. If they succeed*, then the situation will still be “marriage equality”, since there would be no reason to deny heterosexual partners the “right” to have a government-licensed marriage (to add legal advantages to a business partnership, for example).
The problem is that “marriage” has a certain definition: it is a heterosexual union for the purposes of companionship and procreation. That’s clear from Scripture. But even for someone who rejects Truth, the definition of marriage still holds. Marriage is how society manages the bearing and rearing of children. It works pretty well, overall.
In addition, relinquishing to the government the authority to redefine words is unwise. The government always seeks to increase its power over those living within its borders, and the ability to control the language is a key component to its agenda. When people can no longer communicate effectively, then they are more easily divided and suppressed.
*which they apparently will, through the courts; the “debate” over same-sex marriage ended with the defenders of definitional marriage–as a heterosexual union–winning at the ballot box. Their democratic victory has since been overturned in various places by the intervention of Federal judges