A 1st Amendment primer

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof... .

What the above right, the very first mentioned in our 1st Amendment to the U.S. Constitution, says is that this country cannot establish an official religion. Congress cannot pass a bill saying "WE ARE ALL METHODISTS" or "WE ARE ALL RASTAFARIANS" or whatever.
Congress also cannot pass any laws that prevent you personally from being a Methodist or a Rastafarian or a whacked-out evangelical Catholic who doesn't understand what "religious freedom" means. Or from doing the things that those religions espouse provided they are not against any existing law. (You cannot claim you are a follower of Quetzalcoatl and commit human sacrifice.)
Somehow the paranoid ultra-conservative Republican Jesus-freaks have gotten the idea that granting rights to people who are NOT ultra-conservative Republican Jesus-freaks is somehow impeding their ability to exercise their religion.

Rick Santorum thinks that because he is not permitted to force everyone in the country to live by his creed, that we lack freedom of religion. I'd say that his prohibition is proof that the 1st Amendment is doing its job.