The same as it is right now, and has been for years -- the likelihood that people are a danger to themselves or others. The problem at present is that even if mentally ill individuals fit the criteria, there really isn't any place to put them, since the states closed down most of the mental hospitals. So it's not likely that they'll be declared a danger, even if they obviously are because of the potential for lawsuits. And they can't be forced to be treated, so it's a futile effort in any case. Classic "Catch 22". No matter what, everyone loses.
I know several States have that standard, and there are stringent avenues that must be followed after the original assessment is made.
For example, in California the PC is 5150 and is severely limited as to the amount of time an individual can be held pending outcomes of further reviews.
On that level, I can be persuaded but I was actually coming from the Fed level not the State in my concerns.
You make valid points.