For one, 100% enforcibility due to technology, can also just mean 100% enforcibility to THOSE persons those in power don't like. If, for example, you can know immediately when someone violates law X (because of advanced technology), you can still select to apply that to those you want to target only. (One can imagine the McCarthyism government using that knowledge to target "commie sympathizers, or the apartheid govervnemt against blacks, dissidents etc).

(a) some violations being 100% detectable (which is what technology can offer) and (b) fines/jail being enforced to 100% of the violators (which is a policy issue) is a totally orthogonal thing. And since we can't trust policy decisions, I wouldn't like having (a) either.

Second, even if we have (a) and (b), how about when it's not for all laws? (which realistically, it wouldn't be).

If any drug use is immediately detected with some future technology and its use punished, for example, tons of heroin users, who otherwise have done nothing wrong besides possession, would go to jail. And it's not necessary that this will have a big enough backslash to repeal the relevant law (after all, all the marijuana laws that affected millions weren't repealed for decades). To continue with this example, I'd still like most drug addicts to be free, even if the occasional unlucky one is caught.

I don't like perfect 100% systems -- I prefer things to have cracks, is what I'm saying. It's more human.