I'm not sure I follow your line of argument.
I asked you whether you think that it is morally justified to use violence against a person who has harmed no one, but has simply violated a statute banning, say, possession of marijuana?
You respond that, according to me, laws [I assume you mean statute here] cannot be enforced except by interpersonal violence. Is this even a debatable question? How else would statutes be enforced? If person breaks a statute the police (armed men) arrest him. So, first, are you disputing that this is violence?
Also, please explain what you mean when you say mine is a self-fulfilling circular argument.
If you'd like to point out in what way my argument is circular, please do. I'm not seeing it.
The way you presented your beliefs and worded your questions made it circular ...
I am arguing this:
A - It is wrong to initiate (or make threats to initiate) violence against other people and their property. (Technically, by "violence against", I mean any uninvited change to the integrity of a person's body or property.)
B - Because we live in an imperfect world, sometimes violence is necessary. We therefore need to determine when violence is justified and when it isn't.
A & B contradict each other. It either is or isn't wrong. You can't have your cake and eat it, too. The only other interpretation I can see is you're trying to claim two wrongs make a right but that doesn't fly with me, either.
C - I contend that the ONLY justification for violence is AS A RESPONSE to actual (or threats made) initiation of violence to another's body or property.
We've been through threats, already. Again, you have to make up your mind. Either threats justify violence or they don't - but you don't get to decide what a "threat" is. The victim of the threat is the only one that can decide that. Since I'm sure you won't agree with that assessment, we have our second point of contention.
D - All other violence (violence that is not a RESPONSE to initiated violence) is ITSELF the initiation of violence, and is therefore morally unjustified.
E - I then use this argument to determine my support or opposition to any policy or statute. For example, a statute that establishes a punishment for the possession of marijuana would fall into this category. It is an initiation of violence against people who have not themselves harmed anyone.
Just from points A-C you have left open a lot of ground, which is a large part of the problem. Without resolving those issues, it's difficult to move forward. However ...
You seem to have avoided the larger concept of law, to get everyone on the same page (i.e., so everyone knows exactly where they stand) so we can move forward as a civilization. I may not like the laws you think we need, but I'm just as sure you won't like some of the laws I think we need. We need to come to a consensus, one way or another. Your generalizations don't answer how to do that. Even your example is poor because many people feel marijuana is a threat, or rather, that people that are high are a threat. I'm not saying I believe that but that doesn't change what other people believe about it. I don't particularly approve of "victimless crimes" but the ones who support those "crimes" don't see them as victimless at all. They believe gambling, prostitution, and certain drugs are a threat to society as a whole and them individually because of what those people often do. However, I don't see tax evasion as a victimless crime, either, where I'm sure you and many others do. Therein lies the rub.
The result of that, to me, is that we have decided to be a society of laws. As such, whether I feel an action is a crime or not doesn't matter beyond my powers of persuasion to convince others of my position and, of course, my own vote. If we all decide by representation or direct vote that a given action is a crime then, whether individuals believe it's a crime or not, we should all abide by that decision - not because The Man will "come take us away" but because we have agreed to live in a lawful society.
To me, that's the unwritten law people are breaking when they break the laws on the books. They have agreed to live in this society and to live by it's rules. In essence, they have violated their contract and the sentence is expulsion, though they can often "buy their way back in" by paying a fine, instead.