Whether the law exists or doesn't at an international level doesn't matter. In your discussion of state laws applying to an international framework, you are making a false equivalence.
In the case of war crimes and trade law, some effort is put forth by various governments and international courts. Enforcement is available. So to say suddenly that countries can or should do whatever they want within their own legal frameworks is frankly stupid. Lots of countries have much less stable governments than the US. Genocide is a perfect example. If a nation state determined that genocide was legal and started murdering the population, would you simply put forth trade restrictions?
You do know that the US works with Interpol to stop cybercrime, right? That is the very definition of extra-territorial jurisdiction. You seem way out of your depth here, and as I said your ideas seem really poorly thought out.