The First Amendment does not have limits on Freedom of Religion. Over time, Courts have balanced a citizen's first First Amendment rights with other compelling state interests. This is all part of the fabric of what lawyers call the "common law", that is, judge made law.
An early example the balancing act was the limitations on plural marriage. Similarly, the Government has a compelling interest in the health and welfare of its citizens, so it does not allow human or animal sacrifices from groups that practice those rituals.