Your objection makes little sense. First of all, International laws are not some strange set of things. Basically, anything that violates International law almost always also violates National laws. Genocide is multiple counts of murder, War Crimes are torture, rape and murder.
International trade law has some severe penalties in taxes.
International criminal law is focused on the severe crimes I mentioned - Genocide and War crimes. There is NO international law against cyber-crime. That does not mean it has no teeth, it means it does not exist as a law.
In fact international criminal law lets the host country decide to prosecute first. It only goes to the international court if the host country would rather not try the case but want the court to try it. As such, it has SEVERE teeth - capable of imprisoning someone for life. But it has a loophole designed to let the host country have a veto on it. If they use the veto they lose reputation - which has some severe trade penalties - and possibly military ones as well.
Your comment about cybercrime being completely legal is true and pointless. As you pointed out already we have NO POWER TO ENFORCE THAT LAW AS IS, so my proposed rule does not create a new problem. It merely stops governments from abusing their current power.
My idea is well thought out, it simply does not solve all possible problems. Similarly, my idea does not cure AIDS, teach kids to read, or double your lifespan.
The question is does my idea cause more new problems or solve them. The answer to that is that it solves problem.