There is no human right for a person who has been found to be a danger to himself or others to be in possession of a firearm. The restriction could well be temporary, it might even become permanent. But it is not a violation of a human right. Any more than it violates a felon’s human rights to ban them from owning a firearms.
We are going to have to agree to disagree. You have to admit this guy, whatever his mental state, is not accused of shooting up a school.