When someone says "There ought to be a law," ask them this question . . .
"Where's the gun?"
They will probably give you a blank, uncomprehending stare, and say, "What?"
This is the response you want. It denotes confusion. And confusion can be the first step on the road to clarity. Answer their confusion like this . . . "You're advocating a law to control your fellow citizens. But what if they disobey your law? Will an agent of the state point a gun at them and force them to comply?"
Hemming and hawing may commence. Stuff like this, "Well, we won't point a gun at them. We'll just fine them if they don't comply."
"What if they refuse to pay the fine?"
"Then we'll take it from their bank account."
"And perhaps leave them destitute, homeless, or hungry?"
"It's for a good purpose. They should have complied."
"But what if they think their NON-compliance is for a good purpose? What if they think compliance would be bad, destructive, or even evil? And what if they try to promote their vision of the good by hiding their money so that you can't seize it? Does the gun show up then?"
"I'm not sure what you mean?"
"What I mean is this -- If someone doesn't agree that your law has a good purpose, and they refuse to comply with it, and they refuse to pay your fine, and they hide their money so you can't seize it, will men with guns arrive to force them to submit?"
You may get silence and another blank stare, but press the issue . . .
"Is there any point in the enforcement process for your law where agents of the state show up with guns to force obedience?"
If the person is really advocating a law then he or she will have to admit that there's a gun at the end of the enforcement process. Getting to this point is crucial to the task of critical thinking. We cannot think clearly about the nature of The State, and The State's laws, without finding and taking note of the gun that lies behind all Statism.
It's one thing for laws to respond to coercion. That's the purpose of the governmental process. It's quite another thing for laws to initiate coercion against peaceful citizens, based on some scheme of social engineering. Retaliating against violence is the function of government. Initiating violence is the nature of Statism. Finding the gun helps to clarify what is really being proposed.
The question "Where's the gun" should become as well known as "Where's Waldo?" Now here's the final statement in the dialog . . .
"Do you really think your idea for improving the world is so important that people should be compelled to obey it, at the point of a gun?"
The person advocating the law may continue doing so, but because you drew attention to "the gun," he or she can no longer be ignorant of the violence and arrogance inherent in the proposal.