I agree with what Geoff Stone writes in this post.
I have no problem with individuals leading their lives according to their own religious beliefs. If one person needs to wear a yarmulke during the Star Spangled Banner, so be it. If another disdains pork, good for her. If a third has to use peyote as part of his religious observance, fine. If a fourth believes her religion forbids her to marry a woman, I support her right not to do so. But why should our government officially impose one group’s religious faith on others. Should the law require all people to wear a yarmulke, refrain from eating pork, and not marry a person of the same sex? In a highly diverse society that celebrates both its homogeneity and the separation of church and state, government imposition of one faith’s religious practice on others should be unthinkable.
I would caution fellow secularists, though, from thinking the Establishment Clause is the proper mechanism which forbids government from imposing laws which reflect religiously based morality. No doubt our Founders established the US Constitution as a secular document which separates church from state, much in the same way that the Constitution separates powers. But it was not that one little clause in the First Amendment which states "Congress shall make no law respecting an establishment of religion..." that magically separated Church from State and transformed the Constitution into a secular document. Art VI's "No Religious Tests" Clause, the Free Exercise Clause, the 9th Amendment's and the 14th Amendment's Privileges or Immunities Clause's natural liberty rights, Equal Protection principles...in other words, broad substantive guarantees of liberty and equality contained in the Declaration of Independence (the organic law which founds the nation) are encapsulated in the entire document of the US Constitution, not just one little clause. And, ultimately, it is those broad guarantees of liberty and equality which forbid civil government from imposing sectarian dogma on individuals. Case in point -- Lawrence v. Texas was not decided on Establishment Clause grounds, nor should it have been. But that case certainly prevented government from enacting sectarian anti-sodomy dogmas through the civil law, as it should have.