That's debatable (the threat of punishment prevents many of us from breaking the law) but I'll concede.
Even a full ban on late-term abortions would not hold up under your "what if"...as a matter of fact, no anti-abortion law would hold up under that light, or any laws for that matter.
It's not my "what if" it's logical. Furthermore, you're saying that "no anti-abortion law would hold up under that light, or any laws for that matter" is flawed. Laws are supported based on the transgression of acts under the observation of law enforcement personel or a witness. Who is the witness in this case?
Despite my contempt for strawman examples, here it goes...
When a man murders another man he has to have been witnessed by another man and challenged based on testimony in a court of law. Who is the witness in this case? The sworn testimony of the abortion doctor? Hardly a reliable source by any standards.
The law would effectively end the practice for those who do not wish to do something that may bring about legal challenges, the rest will not be stopped by any law.
Where's the legal challenge when the enforcement is circumspect and/or not delegated specifically?