"The right to marry someone you love" may be a stretch - love is a pretty loose legal concept.

However, "the right to enter into a valid legal marriage contract with any consenting adult who will have you" is not a stretch.

You may believe that "opposite-sex" is inherent in the definition of marriage, but I do not see any reason why that would be the case. Insofar as marriage is a religious matter - which isn't very far, considering many people marry in courthouses and civil ceremonies without any religious involvement whatsoever - my church recognizes same-sex marriages as equally blessed. I, my wife, and my child have the same legal marriage needs as a heterosexual family.

There is no valid state interest that makes it make sense for the government to restrict my marriagable pool of citizens to a single sex. Any argument based on child-rearing becomes nonsense when you realize that I and my partner are both equal legal parents to our daughter. Any argument based on religion becomes nonsense when you realize atheist heterosexuals marry legally all the time.