The absurdity of our patchwork of marriage laws

An op-ed in the New York Times highlights the strangeness of America's marriage laws when it comes to dealing with same sex relationships and sex changes:

A lawyer for the transgendered plaintiff in the Littleton case noted the absurdity of the country’s gender laws as they pertain to marriage: “Taking this situation to its logical conclusion, Mrs. Littleton, while in San Antonio, Tex., is a male and has a void marriage; as she travels to Houston, Tex., and enters federal property, she is female and a widow; upon traveling to Kentucky she is female and a widow; but, upon entering Ohio, she is once again male and prohibited from marriage; entering Connecticut, she is again female and may marry; if her travel takes her north to Vermont, she is male and may marry a female; if instead she travels south to New Jersey, she may marry a male.”

The author is a transgendered person whose spouse chose to remain married to a partner despite a legal sex change. I personally know of one such couple in the Bay Area. Given the fragility of so many marriages (especially in the South! :-), shouldn't we be impressed by the commitment that some people are willing to make in the face of challenges that most of us couldn't hope to navigate? Why do so many Americans remain so opposed to just letting consenting adults marry who they choose to marry?