Aren't those who are against same-sex marriage just like those who were against interracial marriage?
The only similarity found in both cases is that large parts of the population opposed the unions. The rationale and the foundational issues are entirely different.
Skin color is irrelevant to the nature (natural function) of marriage, but gender has everything to do with marriage. Since skin color has nothing to do with marriage it was completely illicit for people to impose restrictions because of skin color. The REAL similarity here is between PROHIBITION of interracial marriage and the DEMANDING of same-sex marriage. In both cases you are denying the natural function/purpose of marriage for a political end.
In the case of interracial marriages the intrinsic value found in the natural role of marriage was ignored in order to accomplish a political end (keep blacks from marrying whites). Similarly, in the case of same-sex marriage, the same intrinsic value (future generations/civilization) is being ignored in order to accomplish a political end (the promotion of homosexuality).
Furthermore, treating one race as less than (unworthy of marrying) another race is not Christ-like--"There is neither Jew nor Greek, there is neither slave nor free, there is no male and female, for you are all one in Christ Jesus."--Galatians 3:28 Therefore, those who discriminated against interracial marriages on "religious grounds (while claiming the name of Jesus) were not doing this from anything Jesus taught. No matter what these racists might have claimed with their words, their actions were heretical, and not consistent with the teachings of Jesus.
Conversely, those who DO NOT discriminate against any marriage other than one man and one woman are not doing this from anything Jesus taught. The only marriage that Jesus described/affirmed was the one God designed--one man and one woman. No matter what proponents of same-sex marriage might claim, what they are advocating is heretical, and not consistent with the teachings of Jesus or the Holy Spirit (through the apostles).