Let’s get back to the original question, “Should Aragorn have placed Gandalf under arrest?”
The answer seems clear: yes. Yes, he should have. For then, instead of further tedious footslogging, we could have had an awesome fantasy cop show, featuring Aragorn as the Middle-earth equivalent of the
angry police captain!
(Site generates phrases typifying the stock character, e.g., “The Angry Police Captain just threw his mug at you”, “The Angry Police Captain thinks your partner is getting too close on this one”, “The Angry Police Captain takes it black with three sugars”.)
Much of this is
easily adapted. Thus:
The Angry Ranger Captain doesn’t give a damn about jurisdiction when there are lives on the line.
The Angry Ranger Captain doesn’t have room for screw-ups in the Fellowship.
The Angry Ranger Captain took you off the Moria case.
The Angry Ranger Captain hates to do this, but it’s for your own good.
Try it and see!