Well then that is were you and I (as well as 90% of the public) disagree.
But if that is the negotiating position of the gun crowd (I didn't use the word nuts), then by all means arrest those people. It's more expensive and intrusive and takes away more rights, but hey, it's all about 2A.
Let's play out your little nazi fantasy of taking away guns from a dangerous individual.
You have come into their home. Somehow found every single last gun they have. And left. But you have left the deranged person free. So you already have a mentally deranged person (or whatever term you want to use) and you piss them off by taking their stuff.
So you have now given this unbalanced person a reason to be upset and angry. So they go to their budy, thug on the corner, steal from a neighbor, and now are right back armed (remember it's easier to gets guns than books) and have a motive.
That's not a stream of events that looks to play out well. Ignoring any number of problems in your idea. Person being armed already, not getting all their guns, having one in their car etc etc.
A gun sitting on it's own is no danger. A person on their own is all sorts of danger. You haven't removed the threat by removing the gun. They can take their car, knife, fists and still kill. But of course that doesnt matter to you, you just want the gun.
And you still ignore their due process. At least when arrested there is an established means to this to ensure they still have rights. Miranda rights, lawyers phone call, etc. No such on your gun grab. But please keep ignoring the real problem in order to get rid of the guns.