I think a good way to look at that concept would be to ask outside of having a law on the books just to make a point, how would you be able to enforce such a law without violating the constitution. Could you be able to enforce a law like this without searching without a warrant? Could you be able to substantiate all the elements of the crime you claim to beyond a reasonable doubt...
It is, perhaps, impossible to perfectly enforce any law, with or without violating the Constitution. However, it is clear that an anti-abortion law can be at least partially enforced without violating the Constitution. For instance, one could only prosecute when a woman confesses to performing an abortion.