Most crimes are inconsequential: the perpetrator does not gain very much and the victim does not lose very much. It's doubtful whether it makes sense to report them to the police and doubtful whether the police should do anything about them - well,you might say, it isn't doubtful; the police generally don't.
In many cases, it probably does more harm than good for anyone to be caught and prosecuted, if only because of the waste of time involved and the enormous cost to the public purse. Forced to choose, I would rather that teenage shoplifters didn't get caught - or at least, didn't get dealt with by the police and the Courts. Teenagers will soon grow out of it - only if they don't is some other solution to the crime necessary.
So we should have laws on the statute books which we think twice about invoking and enforcing. It makes for a more civilised society if most citizens don't end up with criminal records.
In some countries, the sense of this attitude is recognised in statutes of limitations: if you aren't caught and tried within a period of time - which may be variable according to the gravity of the offence - then the slate is wiped clean and you can no longer be investigated or prosecuted. You may even choose to admit to the offence at some future date, if it helps you to get it off your chest or helps someone else to know who did it.
The trouble with this approach is that it is open to abuse, as anyone who follows the affairs of Silvio Berlusconi will immediately point out. If you are wealthy, you can employ fancy lawyers to spin out cases until they have to be dropped because they have reached their Expiry date. Law-abiding citizens are then left with the sense that someone who ought to be in prison isn't and only because of his wealth.
This is why other countries don't have statutes of limitations, leaving it to the discretion of the police when to drop a case or decline to open one which just seems very old and best forgotten. That discretion can also be abused, of course. Ordinary citizens guilty of more modest crimes may be less lucky than was Lord Lucan.
In England, we do effectively have a statute of limitations in relation to drug offences. This is what enables our politicians to confess to "youthful experiments" confident that a police constable will not arrive at their door to take down a confession of possession.
In this case I think an Expiry date on the criminal offence would be one way of moving away from the deep freeze on sensible discussion of Drugs law. I can't see that it would give rise to much by way of Berlusconi-style abuse.
Laws should be enforced in moderation. One reason we need to talk about America is that its approach to law enforcement has ended up criminalising a significant part of the population, including a very large proportion of young black males who end up with prison records. It is dysfunctional at so many levels that we should work very hard to avoid it, not least by declining to throw UK citizens to the lions of American justice.