It's a religious practice that as far as I can tell doesn't break any laws or cause enough harm to create a compelling government interest in overriding the 1st amendment,
so, yes that would be an overreach.
Although it's kind of a catch 22 for the Mormons. If they claimed as a certainty that this practice did in fact alter the fate of a person's soul in the afterlife, then you could claim that they were doing something with serious impact on a person without the person's consent...
...then it could be banned. Leave it up to the Mormons to explain it.