The matter is a complex one, of course, [...]
I said nothing more than that.
According to the thoughts behind the Law, you are right, it shouldn't be criminal if there's no offense ; as well as it would go against the constitution if someone tried. But you gave too much power to the court, not enough to common sense, and somehow forgot that all of this is relative.
What I mean is that, in the whole history of a country, you'll not found this many judges ready to force the Law to change. They'll go as I said, using the fact that nobody was able to clearly prove that "this" fall under the law, instead of saying that it's the law itself that shouldn't or can't apply here.
In the same time, the society evolve whatever the Law itself follow this evolution or not. That's where common sense take place, not conducting "this" face to the justice because, despite what say the Law, there's no need to do it nowadays. As for the relativity, it apply because the Law of today is the inheritance of the whole history of the country. What was offensive in the past isn't necessarily what is offensive nowadays.
And that's where the example of criminalized homosexuality serve as good counter example of the theory. When you look closer at it, among the 38 countries where it's still a crime to be homosexual, around ten of them do not apply the sentence anymore ; whatever because the homosexuals aren't prosecuted nowadays, or because, like it was for the US, it's indirectly criminalized ; "Well, you said that they practice sodomy/oral sex, but that's all, you said it, you didn't proved it". Justice do not change the Law, just the way they apply it, as well as the reason why they do it.
As for the offense part, there isn't. I think most of modern people agree with this. Whatever it's directly criminalized or not, there no offense in being homosexual nor there's offense practicing sodomy or oral sex. But it's nowadays view of what is offensive. If you look back at the time where the law was wrote, it's was either an offense to God (sex is for reproduction of the specie), for the country health (it's in 1990 only that homosexuality was removed from the official list of decease). Or for any other reason that would be seen as stupid nowadays, but was perfectly legit at when the law was wrote.
All this apply by example to depiction of illegal subjects, especially the one that goes, or was going in the past, against morale. Back in times, kids didn't had money on there own, nor the idea to buy things by themselves. This mean that laws forbidding to sell, extended to "expose" because they wander in places they weren't going in the past while wanting to buy something else, "this or that" to underage people are in fact recent ; don't take my words on it, but most of them should have less than 50 years. So when, a century ago (or more), it was decided that "this" (incest, bestiality, whatever) is illegal, the law was wrote to include depiction of it. It was their way at this time to prevent exposition of underage people to the act itself in all the possible ways. And when the times come to write a law forbidding to sell and/or expose underage people to "this", most of the time nobody thought that it imply a change that make it a good idea to also rewrite the law banning the said "this".
And when they thought about it, they can have forgot part of the many laws covering the subject. By example, in many countries it's illegal to expose underage people to pornography. That's, more or less, what say the law. They, when it's time to write the law, someone can have thought that they also need to change the law regarding this part of pornography, that one either, oh and don't forget this one... And everybody could have forgot that bestiality is also pornography. This leading to a global Law allowing depiction of any sexual content... except bestiality.
In conclusion, those laws we inherited from the history of our own country still apply nowadays. They can be changed, but there's so many laws and so more important things to change before them, that nobody really care to do it. Imagine your government saying that your law regarding incest is stupid and that it should be made fully legal or fully illegal. I'm sure that you'll hear people saying something like, "what the fuck, it's what you think should be done first ? Have you really seen the state of the country ?"
Most of the time people don't care because they don't ask for justice when they aren't offended, whatever say the Law. And when people feel offended, it's the "offender" which just comply, because he don't want to face justice for something so futile. In the end, the law don't change because it seem to bother nobody that it stay like this.
