Marriage and discrimination?
Take two adults of legal age who have given informed consent to share affection, live together, profess to care about each other deeply, and plan on spending the rest of their lives together.
Explain to me again why the *federal government* has any business discriminating between different couples who do this freely and voluntarily based on their sex organs?
If we're going to talk about families, remember that many heterosexual couples do not, or can not, have children, but we permit them the same benefits as any married couple.
If we're going to talk about the concept of sin, remember that the federal government is not a religious entity and does not make such judgments.