There are so many things wrong with this reasoning, it's kind of hard to know where to start: 1. Take 'Going against legal X yields more illegal X': This is a

There are so many things wrong with this reasoning, it's kind of hard to know where to start: 1. Take 'Going against legal X yields more illegal X': This is a meaningless statement. For example, going against legal murder yields more illegal murder. It is a non-statement, tautological. 2. Take a revised and more debatable statement: 'Going against legal X yields more X' (much rarer, but possible, for example cocaine proliferation brought about by prohibiting less damaging drugs). This deserves careful consideration. Do our laws assume from the outset the required enforcement to enable their utility? In some ways yes, in other ways no (for example, our laws shouldn't need to take into account politically motivated lack of enforcement). 3. Even if we say that a particular law leads to _more_ of the exact averse outcome and the legislature should have known the challenges of enforcement - illegal drugs being a good example of this, or illegal immigration, it _still_ doesn't follow in all cases that the answer is to decriminalize. A debate must be had, for sure - and some change is required, but that change may be subtle, enabling better enforcement for example. However, your above logic as it stands is essentially an argument for anarchism, though I'm not sure you intended it that way.