Our culture has become grasped by two important connected ancient doctrines, which are deeply illiberal (indeed, in my view frightening) in their implications. One doctrine is that our behaviour is fundamentally a reflection of our nature, our character. Whether you are a criminal or religious or a homosexual, your conduct is said to be the result of some combination of your genes and your upbringing – nature or nurture. We have seen this most recently in the many outraged articles published in response to the proposed "post-gay" bus adverts, which declare "there's no such thing as a 'gay cure'", but an idea that has been around for some time and embodied in documentaries asking questions such as "What makes us gay?" Similarly, there are angst-ridden debates in some circles as to whether those with the "religion gene" are out-breeding the rest. Again, whether we become criminals is now said to be strongly related to whether we carry genes for criminality.
The second doctrine is that it is hypocritical, and thus bad or self-destructive, to act against one's true nature. Indeed, more than that, it is one's true nature and motivations that really matter. If you are a politician, we are not interested in whether your tax cut for the rich is good or bad for business and general prosperity – what we care about is whether you personally gain from it. If you are unhappy in your marriage and have fallen in love with someone else, we say you ought to leave your spouse and go off with the other person (especially if the other person is the same sex as you) rather than keeping your vows. The notion that there might be merit in aspiring to conduct oneself according to a theoretical ideal, rather than to one's current tastes, is considered, if not actually impossible, definitely a bad idea.
We might summarize this doctrine by saying that the true person, the real you, is defined by your appetites and feelings, not by your deeds or aspirations. This is actually a very ancient claim, going back to at least the ancient Greeks (probably well before). The idea is that excellence, virtue, resides in your character, and your behaviour is simply a reflection of that internal degree of excellence.
If we believe that, or if we do not take it literally but instead see it as the healthy norm, there are important implications. It will then be either pointless or bad to encourage people to act against their natures. And because everyone is to act in accordance with her nature, we would become very careful about whom we had around us – it would become very dangerous to associate with those of wrong character. If technology allowed, it would become very tempting to ensure that we only permitted those with the characters we wanted into our society – whether by doing genetic testing as part of immigration or by selecting our offspring either through controlled insemination or abortion. We would also weight the evidence of past behaviour very highly in inferring future behaviour – the idea that someone could be truly a reformed character would be silly; instead we would need to be persuaded that any aberration had been fundamentally out-of-character or had reflected special circumstances. If your behaviour violates the preferred group norm, you are likely to be an ongoing and unwelcome irritation to society. After all, it is not as if you could usefully "convert" anyone to your way of looking at things or persuade them of the fundamental "truth" of your approach – each of us is simply behaving according to our set and inflexible nature. You cannot improve society; you can only disrupt or overturn it.
This ancient doctrine has faced a rather more recent (more "modern", if you like) competitor: orthodox mainstream Christian doctrine. This alternative idea makes two really radical claims: first, that we do not have to behave according to our basic natures, and indeed it can be undesirable for us to do so; and second that the true person, the real you, is not defined by your appetites and inclinations, but instead by your aspirations and your faith.
There was always understood to be a difficulty here, in the claim that (at least in any sustained way) we are able to behave against our natures. In some variants (e.g. that of the popular Christian writer C.S. Lewis) it is claimed that a key form of "faith" is the faith that if we are persistent and disciplined in our efforts to act according to our aspirations (our beliefs), our natures will change (perhaps miraculously, under the influence of the Holy Spirit) such that we find it easier to act according to aspiration and less tempting to act according to nature. This process is sometimes called "sanctification".
An alternative mainstream Christian view was that we will always inevitably face a desperate struggle between our appetites (our "old man") and our aspirations (our "new man"), but that although our appetites may never change, with discipline and under the tutelage of the Holy Spirit, we can master them and make them our servants instead of being their slaves. In other words, pace Lewis, it may never become less unpleasant to act according to our aspirations but we become more practised at doing so.
This doctrine implies a very different social order and investment of meaning in people. What really counts, now, is not our character – not how we happen to be now – but our aspirations – what we aspire to be, under the transforming guidance of the Holy Spirit. The true person is the acter, not the feeler. So if I discover that someone's personal conduct is at odds with her public statements, that might be because she is a liar, but it also might just be because all of us face a struggle. The Christian is therefore much more likely to be sympathetic of misdemeanours and much more optimistic that people can change, permanently.
This also means that one will value diversity of outlook much more, including in particular outlook with which one disagrees. Because what really counts is that my aspirations and beliefs are true, and someone with a different set of beliefs might be right and I might be wrong, and if that is so then I can change – my true person is not fixed. And it is really important that people should not only be permitted to hold divergent (and wrong) beliefs but also that they should be able to express them – a liberal society must be tolerant (i.e. live with what it disagrees with) not simply accepting (disagreeing with nothing it permits). There will also be no dud people – no-one's character is such that she is permanently lost; permanently valueless – her character isn't the key thing, and never was. And similarly no-one should accept her own character as the final word.
Thus when someone says "Folk should not be permitted to criticise my conduct, as I am incapable of behaving otherwise", there is a lot at stake – an entire vision of society. No mainstream Christian could ever accept this, and if one wants to allow mainstream Christians in one's society, that Christians will not accept this is something one really must get over.