The advice to "use it or lose it" is usually applied to brainpower; we're urged to keep our minds active, since that really does help avoid the pitfalls of aging. However, it could usefully be applied to legislation as well. The rest of this entry is behind a link because you may not wish to read it at work.
It's probably clear by now that I'm not a fan of far-reaching legislation; I prefer to trust people to get on with life and not be too frightful to their fellow man. I also realise that there are situations where legislation really is useful. However, every jurisdiction has some obsolete laws, or some laws which are no longer enforced, if they ever were.
Such laws are beartraps. Any law which is not being consistently enforced is a bad law; it allows latitude for arbitrary abuse of policing powers. Let's take the infamous law regarding London taxis as an example; it is required, technically, that each London taxi carry a bale of hay, so as to allow for the feeding of the horse. Given that horses are no longer a feature of the typical London taxi, one would assume that the law ought to be repealed; it has not been. However, it's not commonly enforced. There is, unfortunately, no way to prevent any police officer from taking against a taxi driver, and successfully prosecuting him under an obsolete, nonsensical law. Sadly, relying on common decency isn't enough; it's a petty thing, and humans are very good at being petty. Since the law is not being consistently enforced, it should be repealed.
Another fine example group is the laws in various US states regarding sodomy. Generally, these define sodomy as any sexual behaviour other than penis-in-vagina, which is very silly; this would have made my first sexual experience criminal in these states, despite both parties being consenting adults, because that experience consisted entirely of me performing oral sex. While the intent of the law was to criminalise those dirty gays, it also criminalises normal sexual behaviour in heterosexuals, and I have no doubt that the authors of the various bills were not averse to oral sex being performed on them. This is also a case where the lack of a statement of intent has led to potential problems.
Now, when it comes to legislating morality, I'm agin it. Sexual behaviour isn't a fit subject for the law so long as nobody is suffering damage. If everyone's getting off, then go right ahead. Marriage? If all parties involved are able to consent and fully understand what they're getting into, go right ahead; we have contract law that covers these things.
But any law which is inconsistently enforced, or not enforced, can and probably will turn around and bite you in the bum. So enforce them properly, or get rid of them!
Maybe that way we can stop committing felonies. It might even become possible once again to know what is and isn't legal.