The first Amendment provides that "Congress shall make no law respecting an establishment of Religion, nor prohibiting the free exercise thereof..."
Practically, this means that if you choose to practice a religion in this country, you are free to do so, and if you choose to not have a particular religion or religious doctrine foisted upon, you have that freedom as well. Over the years, this First Amendment has been found to apply not just to the Federal Government, but also to the states, incorporated through the 14th Amendment.
There have been a few Court cases that have provided some (not crystal) clarity on the meaning of the First Amendment, including the oft-cited (by me) Lemon v. Kurtzman, 403 U. S. 602 (1971) which explains how a proposed act would not be violative of said Amendment: (it must have) 1. a legitimate secular purpose, 2. a pimary effect that neither advances nor inhibits religion, and 3. the statute must not foster an excessive government entanglement with religion.
Additionally, we have Justice Black's explanation of the First Amendment in Everson v. Board of Education, 330 U. S. 1 (1947), in which he states,
The "establishment of religion" clause of the First Amendment means at least this: Neither a state nor the federal government can set up a church. Neither can pass laws which aid one religion, aid all religions, or prefer one religion over another. Neither can force nor influence a person to go to or to remain away from church against his will or force him to profess a belief or disbelief in any religion. No person can be punished for entertaining or professing religious beliefs or disbeliefs, for church attendance or non-attendance. No tax in any amount, large or small, can be levied to support any religious activities or institutions, whatever they may be called, or whatever form they may adopt to teach or practice religion. Neither a state nor the Federal Government can, openly or secretly, participate in the affairs of any religious organizations or groups and vice versa. In the words of Jefferson, the clause against establishment of religion by law was intended to erect "a wall of separation between church and State.beyond this we have a few other cases that touch on the First Amendment, see e.g. Lee v. Weisman, 505 U.S. 577 (1992), Santa Fe ISD v. Doe, 530 U.S. 290 (2000), and Epperson v. Arkansas, 393 U.S. 97. One of the best resources for studying the history of 1st Amendment Religion Clause history is Kitzmiller v. Dover Area Sch. Dist., 400 F. Supp. 2d 707, which I encourage those interested in Religion Clause issues to read at least once.
Now that I've gotten the brief history that I said I wasn't going to get into out of the way, let's get to the crux of this post. What I'm looking at this morning is a quote by a member of the American Family Association, who has claimed recently that "Islam has no fundamental First Amendment claims, for the simple reason that it was not written to protect the religion of Islam. Islam is entitled only to the religious liberty we extend to it out of courtesy. While there certainly ought to be a presumption of religious liberty for non-Christian religious traditions in America, the Founders were not writing a suicide pact when they wrote the First Amendment."
If we go back and look at the legislative and Court history, we can see very easily how wrong-minded this notion is, but in order to combat untruths like this, we need to explain a lot. This is what makes untruths so dangerous - they are quick soundbites that (may) seem to pack a good amount of information in them but the explanation afterward takes so much longer to get through that people don't want to hear it.
I don't begrudge people their opinions, but before spouting off on those opinions, particularly of Constitutional Matters, I wish people would do their homework.