It is unfair and against the first amendment to give preferential treatment to married individuals. Marriage is a creation of the church and individuals that do not follow the church should not be required to follow a doctrine that they do not believe in to get things such as tax breaks.
Instead of tax breaks for marriage we could give tax breaks for people who care for children, this way we could balance out the impact to families with children while not giving undeserved tax breaks to two people that do not have children.
This would nullify most if not all of the arguments about same sex marriage, since they would gain nothing beyond recognition from their church for their union.
Last, we should make it illegal to give preferences to married people just as we do for sex and race.