Presume them repressive
One of the jewels of Western society, which it can justifiably feel proud of, is its means of administering justice. Due process, trial by a jury of one's peers and the proper presentation of evidence are tools to safeguard the citizen from malicious prosecution and harassment by the authorities. How they have survived so long is a mystery. The cornerstone of the process is the presumption of innocence. Your accusers must prove you guilty of an offence. This alone prevents the authorities from putting you away on trumped-up charges (a presumption of guilt leaves you in the awkward position of having to prove a negative, and we all know how difficult that is).
The UK government hates civil liberties. It has been busily denying rights to immigrants -- illegal or otherwise, asylum seekers and foreign citizens (some of whom have been locked up in Belmarsh, without trial, to our great shame, for more than two years), and now it is moving on to citizens.
Their latest wheeze is to have previous offences revealed to juries. This, they say, will lessen the number of guilty kiddie fiddlers who walk.
However, it is quite clear that this at the very least damages the presumption of innocence. Say I am on trial for punching my wife. If the jury is told that I previously did three months for punching her a couple of years ago, they will, of course, presume I am guilty of the new offence. I am left in the position of having to prove I did not do it, that I am reformed, whatever.
Another important brick in the edifice of justice is that the evidence in a case must belong. So, generally, the defence cannot use the victim's sexual history in a rape case because it is not evidence about the rape. It's clear to see that evidence of a prior assault is not in any way evidence in a current case. (Yes, you can argue that it shows a disposition to assault but the very thing that I am concerned about here is that the prosecution is using a previous conviction as proof of recidivism. It is one thing to say "you often lose your temper and that might lead you to hit your wife" and another to say "you were convicted last year so you must have done it again").
Yes, I know. In nearly every case, the accused will be repeating the dose and will deserve to go down for it. In nearly every case, even if thin evidence will be padded out with mention of prior convictions, the accused will actually be guilty and no harm will be done.
Or will it? What about the bad boy who really has reformed? What about the rapist who was sent down five years ago, the new "victim" knows it, and is falsely accused this time? Does he not deserve the protection of the law because he once did a bad thing?
It is precisely in these cases that justice must fiercely be protected. What makes our system so valuable, something we truly can feel proud of, is that it is for all. Because we will defend the rights of the worst, we know that we, who are not so bad, will have ours protected too.