In order to address this issue, one must first define the concept or meaning of marriage. However, this is a rather subjective approach, because the way we define marriage depends on our own views and interpretations.
To come straight to the point, I believe that there is no difference between same sex and traditional marriages regarding validity or moral implications. One could argue that the bond between man and woman is valid, since biologically they are able to have a child. This would go along with scientific theories such as evolution. Yet, man is not an animal. Mankind has elevated himself to a point where we do not rely on instincts, but use our brains in order to survive.
Love is a phenomenon, which is purely human. Hence, if two individuals of the same sex love each other, why can they not celebrate this love through marriage? Biology should not be an argument against this.
Furthermore, the word "equal" in section 1 of the 14th amendment implies that everyone should have the right to get married no matter what his or her sexual preference. Marriage is the legal and public documentation of the love and trust two people share for each other. This means that anyone should be able to marry whomever he or she wishes.
Obviously this does not correspond with traditional or even some contemporary views of marriage. Yet, is the traditional marriage really so sacred in our society? Today divorce rates are so high, that it is not uncommon to remarry two or three times. Hence, does our society actually have a right to criticize same sex marriages when marriages in general are not taken seriously?
Furthermore, the point that marriages play an important role in reproduction is also debatable. As mentioned above, high divorce rates cannot possibly be a healthy environment for a child to grow up in. Additionally, children will grow up with a lack in family values and continue this trend (high divorce rates) during their adult lives. Moreover, there are so many orphans around the world, that couples should consider adopting as an alternative to having a baby. Therefore, if a gay family would want to make a family out of their marriage adoption could be the answer.