While I agree that the state/government has no place in marriage, that is not clear in the constitution. If a state wants to define marriage they have that constitutional right, whether I agree with them or not.
The 10th Amendment to the Constitution says " The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."
States defining marriage operate off of a negative. They do it because marriage is not defined. Notice is says reserved to the States or the people. Does it not seem odd that all 50 states presume the power to define marriage?
Marriage was instituted by the Lord as recorded in Genesis. It is clearly defined, and does not include same sex marriages. The Framers of the Constitution had sense enough to leave the issue alone. The Lord does not need help in giving the sacred instititution of marriage a helping hand. The fact that state governments have chosen to define marriage cheapens the institution itself.
When the Lord instituted marriage, it was an eternal standard. One man, one woman, for life. Really deep stuff there. The Bible is quite clear about marrying someone built like you, or exchanging vows with your cat. So, state governments, presume to pass laws that define marriage like the Bible, with one difference. God's standards are permanent and eternal. State government's standards are subject to change and in our case, seem to last a little over 200 years.
To agrue that states have the power to define marriage requires exercising an unmentioned power, AND denying that unmentioned power to the people. The 10th Amendment says states or people.
In the reality of the situation, one can certainly not argue against your position, as it is a physical fact that fifty laws defining marriage do exist. When mixed with the sacred, government is disguisting, so in reality, it makes no difference whether the state or federal government infects marriage.