There is not a lot of explanation here. What is meant by the gay couples not having the same benefit? Anyway the ethical principal of not treating anyone differently seems sound when one imagines it in some contexts, but is absurd when one extends it to a general principle without restriction of context:

For example, let us say some innocent person is shot, the people in the ambulance rush to them and take them to the hospital...but they don't treat people who were not shot the same way...they ignore them if they are not in the way, and they expect them to move out of the way if they are. All of this is perfectly reasonable ethical behavior...but certainly the people are being treated grossly differently.

Now one might object to my analysis and say I am applying the principle of fairness in the wrong way. Rather the principle really is that the ambulance should rush to those who were shot independent of who that person might be, being that the people themselves are of equal importance to be tended whenever there is dire need of such tending.

But then some people will not ever need an ambulance and some people will need it more than once. So the principle of having ambulances will serve some more than others. Suppose there is somebody who is invulnerable and healthy by nature. They will never get to ride in the ambulance unless the policy is changed. They are necessarily treated differently. And yet on account of this, the ambulance crew can't be said to be unfair or unreasonable. For the purpose of an ambulance is to take care of people that need emergency care.

When things have a purpose, like ambulances and marriage for that matter, then it does not become necessarily unfair to treat people differently in regard to their relationship with that purpose.

The purpose of marriage as a social and biological structure has been to promote healthy reproduction. This does not mean that a particular couple who are not fertile should not be allowed to marry. The fact that they are not fertile is really nobody else's business. But it does mean a man should not marry his sister. That structure or tradition is bad for healthy reproduction. The traditional policy of recognizing marriage between any adult man and woman who do not have other mating obligations to form a bond and agreement to only mate with each other, but not allowing it if they are too closely related by family line, is a good one.

Its not perfect, but its good. Now there is more to marriage then simple reproduction--there is the bond between the adults and the affections of romantic love and more firm kinds of love that grow out of it. These bonds can be formed by homosexual couples. In this respect homosexual partnerships resemble marriage of infertile couples. But there is on this account no good reason have to call these couples marriage and to have society forced to drop the distinction and to have policies toward such unions identical to the policies toward marriages.