I don't see why you think it's a dishonest characterization. You don't think the regulation of money exchange is constitutional, I think it is because it's a commercial activity and the commerce clause of the constitution empowers Congress to legislate on such things - it's one of the enumerated powers, as popposed to being inferred by courts. As I'm sure you're aware of the commerce clause the only logical basis I can see for your position is if you don't think money exchange is a commercial activity.

Also ad hominem means something other than what you seem to think it means. That's when you dismiss someone's argument by saying there's something bad about the person making the argument, eg 'ignore what Alice said because she's a communist.'