People should only be allowed liberty if it is used responsibly. It's the same reason I support criminalising holocaust denial and oppose legalising polygamy. If your rights are used for nefarious purposes, then they must be denied. We cannot let the likes of Charles Mason or whoever runs Scientology do what they want with their cult members in the name of religious liberty.
Freedom of religion is heavily valued in the United States, I respect that. But when people harm others, or deny them their civil rights and use their religious beliefs to justify it, they are crossing the line. Freedom of religion is not absolute. Take Warren Jeffs (leader of the fundamentalist Mormon church) for example; he thought his religion entitled him to marry underage girls and sexually assault them! And when he was standing trial, he was complaining that his religious rights were being trampled on.
Religious liberties, like any other liberties, only extend to the point where you are violating other people's rights.
If you are making the choice as, for example, a jehovah's witness refusing blood transfusions, you are making a free choice about your own health care. Totally protected. But should that extend to minors with parents who are Jehovah's witnesses, and who have not yet reached the age of majority?
You can wish for the spread of Islam, and preach whatever you want, but the doctrine of conversion by the sword is not acceptable, as that is the limit of your religious liberty. Pretty straightforward.