You seem to have in mind a specific legal prohibition. None comes to my mind, other than the obvious standards of good taste
which obviously don't apply to the Trump administration.
- piffle -
Government can do all sorts of things the rest of us can't.
Police cars can exceed posted speed limits, run red lights, etc.
Government can incarcerate. We can't.
Government can tax. Don't even think about it.
It would be nice to live in a world where there were no bad guys worthy of 25 to life sentences, or worse. BUT ! ...
I totally disagree.
Police cars should never conduct high speed chases legally.
But clearly the fact ambulances also exceed posted speed limits, proves anyone can if necessary and with appropriate lighting.
It is not a function of government.
We can and do incarcerate privately.
The Walmart security guard apprehends, and remote locations, will also incarcerate for periods of time.
Essentially all land lords are just taxing residents.
It is not about a "specific legal prohibition".
It is about the source of legal authority.
Which is the defense of inherent individual rights.
In a republic, government only borrows the authority we delegate to it.
We are the source of all legal authority, from what is needed in order to defend our inherent rights.
So then if we can not do it, we can't delegate it to government, so then government can not do it even more so.
The fact individuals do not do things, like incarceration, is not because they legally can't, but because it protects the rights of all better if we refrain and let government do it in a more regulated fashion.
But if someone commits a murder in some remote place, and there is no other safe means, then the people there could privately give a trial and execution if necessary.
But as long as it is not a remote place and has prisons available, there is no source of authority for republic governments to execute.