The government certainly /can/ tell you "how to care for a member of your tribe" if that member is a minor. The ritual circumcision Hitchens references led to a small but deadly outbreak of herpes among recently circumcised babies. The government should let /adults/ practice their religion as they choose, but there would certainly be a rational basis for concluding that this particular practice unnecessarily endangers a third party: children who lack the ability to say, "No, thank you! I'm Buddhist." The same goes for Christian sects that disapprove of medicine. Sure, adults can turn down medical treatment for /themselves/, but if they do so for their children they could (and should) go to jail for child endangerment. A civil libertarian should want to protect everyone's right to liberty, the right to do whatever they wish /without harming others./ In these cases, the religious parents' choices often do harm their children, who are too young to object.