Professor Jon Tonge's masterly survey of the DUP makes it clear how narrowly based our political class is.
In the case of the DUP, the over-representation of Free Presbyterians and Orangemen in elected politics is striking. Seventy-five per cent of MPs, for instance, are in the Orange Order. The flipside is that other groups can easily be sidelined.
Overall, there are too few women in politics and there are only a handful of members of ethnic minorities in elected positions. There are just four openly gay councillors and no openly gay MLAs, though that is nowhere near the proportion in the populations as a whole.
Some will argue that this doesn't matter. The important thing is getting the most able elected representatives available, not ticking boxes for the sake of filling quotas.
There is some truth in that, but can anyone say we really do have the best political representatives available in all cases? How many of our 108 MLAs would earn the sort of money – a minimum of £48,000 – they get at Stormont elsewhere? Some would, but we all know a great many wouldn't.
The perception that politicians are generally drawn from particular social groups discourages others from either voting, or putting themselves forward for election. People feel they wouldn't fit in and turn their backs on politics, which can be regarded as a dirty game, or a bit of a joke.
The over-representation of certain groups, for instance former IRA prisoners in Sinn Fein, also creates a certain clannishness that leaves politicians blindsided to the implications of what they say.
I don't believe that Peter Robinson considers himself either sectarian or racist – quite the opposite. Yet the fact that he is in a party whose political compass is set by white, born-again, male heterosexuals can't prepare him for how statements go down with groups as diverse as gays, women or Muslims.
He attended Pastor McConnell's church and worked closely with Ian Paisley snr for many years. No wonder he didn't think it was anything out of the ordinary for a preacher to describe other religions as Satanic or spawned in Hell. No wonder Nigel Dodds, his deputy and a man who has worked to help racial minorities, thought it was all right to make such remarks provided they were scripturally based.
The problem is that there is enough in scripture, whether the Bible or the Koran, to justify almost anything, and much of it will be offensive if openly advocated. "The devil can cite scripture for his purpose," as Shakespeare put it.
In any case, saying that Islam is the work of the Devil can't be strictly scriptural, because Islam didn't exist as a religion in biblical times.
It is unacceptable in public discourse to use this sort of language – just as it would be unacceptable to demand, on biblical grounds, that adulterers be put to death, or that believers have a duty to immediately kill anyone who suggests they serve other gods (Deuteronomy 13: 6-11).
That would be hate preaching and should be considered unacceptable – but people can be blinded to the offence caused by their backgrounds. In much the same way, Gerry Kelly and some other Sinn Fein members can be surprised by the reaction that some of their statements get from IRA victims.
It is easy to put your foot in it if you listen only to people who come from a similar background, often a minority opinion in the wider society.
If our big parties don't broaden their recruitment bases to reflect the society they seek to represent, they risk losing touch and being gradually eclipsed.