But you are right, those convicted of crimes can choose jail or a boot camp, then as long as both are run humanely I have no problem with it.
The issue is whether parents have the right to hire people to punish, indoctrinate torture, brainwash, abuse, rape, humiliate, beat, isolate, kidnap, or otherwise harm their kids. I think most people on this list, and quite possibly a majority of the general public would agree that parents do not have that right, that their are limits to parental power over their kids, and that the kids as human beings and citizens of the United States have fundamental rights, and among those rights is the right to be treated with dignity. I would argue that children and teens have the right to not be kidnapped, brainwashed, tortured, indoctrinated, abused, beaten, raped, or humiliated, whether it is supposed to be "for their own good" or not.