Because human sacrifice is a religious belief that has existed and could exist as a part of religion. It is extreme, but still an example of where the Constitution limits people's religion. Another would be in the consequences of actions (which I did mention and you ignored) for sins/wrongdoing in many religions, which include killing people for various offenses. And yes, those are in the Bible.
Actually, you are wrong, we do restrict people in the "free exercise" of some beliefs. If someone feels that the Bible compels them to kill homosexuals or witches (and they view practicing Wiccans or palm readers as witches) or that the Koran compels them to beat their disobedient wives or kill their promiscuous daughters or sisters, they are prevented from doing those things by our laws that are based on religious beliefs.
And here are the verses that support those people who might believe those things:
Exodus 22:18 - Thou shalt not suffer a witch to live.
Leviticus 20:13 - If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them.
Heck, apparently President Obama's own grandmother believes that beating disobedient wives is okay. And this, although a relatively minor belief at least here in the US, is still a belief in many different religions, including some fundamentalist Christian sects.
My respond to the so called "Wife Beating is allowed at anytime" lie against Islam:
And while there are plenty of honor killings outside of Islam, and they are denounced by many Muslims, especially since they are not reportedly condone by the Koran, they are still seen by too many Muslims as a religious necessity to maintain family honor.
