One of the biggest issues concerning this argument is the public display of the Ten Commandments. Okay, I understand that if you don't believe in a Supreme Being, or believe in a different one than Christ and the God of Abraham, you could take issue with numbers one through four. But who could object to everything between "Honor your father and your mother" to "You shall not covet your neighbor's stuff"? Every religion has the same basic rules of morality, like "You shall not murder" and "You shall not commit adultery."
Why do people object? Well because:
A.) The ten commandments are part of the christian rule book, they are not the law of the land, as you probably noticed, since committing Adultery is not criminal and not honouring your parents isn't a crime either. Therefore, it's very obvious, that the ten commandment are not the basis of the law. They may have a few good ides one can take (like: thou shall not murder) but in their entirety they are not important.
B.)A courthouse, is a state institution. The state is by the constitution bound to not endorse a religion. If a display, that is clearly christianity based, is shown inside a state institution it becomes a de facto endorsement of said religion. This leads to a direct deterioration of the trust other religions or non-religious people have into state institutions, which means a de facto weakening of Authority for these institutions. Oh, and please don't distort the truth, the ten commandment incident was not about a public display of them it was about a display of them INSIDE a courthouse. It's really very easy. I as an atheist for example would not trust a court to handle my issues, if he shows this kind of favouritism towards christianity.
C.) Since there is the “non-endorsement clause” there is only one way to make sure that you could display the ten commandments in a courthouse without endorsing christianity and that is showing the RELIGIOUS rules of all religions (not even only the major ones). So, you would have your precious ten commandments next to islamic rules about eating pork and Buddhist rules about harming even insects. This is nice and dandy if you want to make an exhibit about “Religious Rules of the World” but we're in a friggin' courthouse! If you want that go to a museum for Darwin's sake.
Besides, "separation of church and state" isn't even in the Constitution.
Wrong, the non-endorsement clause implicitly is separation of Church and State because a non-endorsement would be de facto impossible if Church and State were not separated. The Treaty of Tripolis states it even explicitly
As for the gay marriage and abortion issues, most religious people I know don't want to "cram our beliefs down your throats", as many like to say, but wish the issues voted on by the people and the legislatures instead of having Supreme Court Justices "cram their opinions down our throats," because they have legitimate concerns over these issues. Then, if you want to allow or disallow abortion or gay marriage, you may simply vote yes or no.
No, they really have no legitimation on it, because they are not manoeuvred into a position were they HAVE to take an abortion or marry a homosexual. Both things don't tangent the lives of religious people the slightest or change their lives even a little bit. As for the Supreme Court argument. You may have noticed that there is nothing in the Constitution that says anything about marriage. It states, however, the right to the pursuit of happiness, whatever that is. In case of a Homosexual person, I'd wager it's the desire to be together with the person he or she loves. Therefore, state bans would be in direct hindrance to that right and therefore be unconstitutional. Ergo, it's not only the right but the obligation of the Supreme Court to trash state legislation to ban gay marriage. The rights of the constitution are not up for "majorities vote". They must be enforced even against the majority, if necessary. Now, this whole discussion about a constitutional amendment is legitimate, however, the reasons are not. It's outrageous that people want a change to the constitution because a non-criminal behaviour collides with their religious believes. It shows a severe lack of respect for the integrity of the Constitution itself, to individual rights, to human nature and a lack of respect to people, different than oneself.
As for Abortion, that's another issue, however, in my opinion, prohibiting it out of religious reasons will cause much more harm to all the people involved than it will do good.