It is because life isn't fair that the constitution requires it of the law. Whether you choose to be fair or not, the law has no choice.Life is NOT fair. Get over it.
"Congress... cannot deny the liberty protected by the Due Process Clause of the Fifth Amendment.
...the principal purpose and the necessary effect of this law are to demean those persons who are in a lawful same-sex marriage. This requires the Court to hold, as it now does, that DOMA is unconstitutional as a deprivation of the liberty of the person protected by the Fifth Amendment of the Constitution.
The liberty protected by the Fifth Amendment's Due Process Clause contains within it the prohibition against denying to any person the equal protection of the laws. While the Fifth Amendment itself withdraws from the Government the power to degrade or demean in the way this law does, the equal protection guarantee of the Fourteenth Amendment makes that Fifth Amendment right all the more specific and all the better understood and preserved." (Windsor)