Except you were obviously not using the phrase in that sense? There is absolutely no contradiction between "objective" and "taking into account many details of the individual case". There is absolutely no problem with writing a law that objectively specifies that the punishment for "17 years and 364 day" is going to be only marginally worse than for "18 years", for example, which you used as an example for why a "bright and clear line" would be necessary, and that that would mean that you have to have to have a strict cut-off point between hard punishment and no punishment at all.

> There is. Just because something is not consistently enforced doesn’t mean it’s not clearly illegal. Cops may not fine you if they see you jaywalking, but you’re still unambiguously breaking the law if you cross the street outside of the crosswalk.

In other words: There isn't. If you are breaking the law, but there are pretty reliably no consequences, in which sense are you then breaking the law that would be relevant to this discussion?

> Most crimes (although not statutory rape) require intent to be shown [2].

In other words: For most crimes, there is less of a "bright and clear line", and things generally seem to be working well, or even better. So, how is that a justificaton for having more of a "bright and clear line"?

> No justice system is perfect; innocent people get convicted and guilty people go unpunished.

Well ... sure? I am not sure why you mention that?!

> A good law should allow people to unambiguously know when they would break it.

I am not sure I would agree with that. I mean, yes, ideally, people should be able to know in advance what would constitute breaking a given law and what would not, sure. But the problem I see is that this ideal goal is in conflict with other goals of a legal system, such as being just. And "bright and clear lines" in the sense in which you are using the phrase tend to have very nasty side effects in that regard, because they massively increase the probability that honest mistakes that harm noone are punished the same as premeditated harming of another human, but also that someone intentionally doing harm that just so happens to be on the legal side of the "bright and clear line" goes unpunished.

So, I would agree that laws should be as objective as possible in describing what is illegal. But at the same time, circumstances should always be considered so as to avoid injustice that results from overly simplistic rules being applied. That doesn't mean that judges should make arbitrary decisions, though, in that there is no problem with at least attempting to codify the details of how to justly judge individual cases rather than settling for the simplest rule possible. While you might never be able to codify all the possible things to consider, that does not mean that the only other option is to make a simplistic rule.