We should not ban any religion that practices self harm as long as it is not affecting anyone that doesn't want it, is not brainwashing people, and is not breaking any laws. The freedom of religion in this country is too great an issue to try to ban a religion.
We should encourage reform and take steps to protect the vulnerable, but competent adults who are harming no one else have the right to control their bodies.
Making certain practices illegal is, however, within the bounds of acceptability. The criteria for such laws would of necessity be high. The practice would have to have a high risk of resulting in death, a potential to injure or kill others, or cause significant disruption of the lives and/or civil rights of other persons.
A good example would be if a religion sprouted tomorrow that claimed smoking meth-amphetamines was the only way to get closer to God and necessary to their belief. Since the manufacture of such drugs inevitably results in highly toxic by-product which can contaminate a structure for years, that alone is reason enough to ban this hypothetical religious practice. (There are, of course, many other perfectly serviceable reasons why meth-amphetamines are illegal. I will not list them all here.)
Individual religious practices have been banned in the US before, some for legitimate reasons, others for debatable, controversial, or openly discriminatory reasons.
The problem with banning religions is that religions do not throw stones. People do. Religions do not mutilate people. People do. Punish the wrongdoer and you curb the behavior. Suppress the entire religion and you spark a rebellion, or at the very least create even more criminals than you began with.
I think anybody should be able to practice their own religion, because it's a freedom. If someones religion involves causing harm to themself and they die because of it, then it's natural selection. CLEARLY if someone has decided to follow a religion that involves causing harm to themself and possibly death, then maybe they're supposed to die.
As long as their no forcing children to hurt themselves, no it should not be up to anybody except them. They are not hurting anybody besides themselves and their doing it behind their closed doors. I don't see how it's anybody business expert theirs. I don't think government should regulate religion and vice verse.
The individual should decide how best to achieve his or her own spiritual goals even if it conflicts with society's norms. There are those who practice such things as self-flagellation which I myself see as having no value but who am I to judge? Now if they start practicing child-flagellation then we can talk.