The stronger the Christian Right, the less attracted people are to religion, according to a recent US study.

It makes fascinating reading. In states where a lot of non-profits start campaigning against gay marriage and abortion – causes dear to the hearts of conservatives – people are more likely to answer 'none' when asked about their religious faith. And it is a delicious irony that the groups most likely to be passionate about these causes are also passionate about evangelism. If they make it harder for a tiny number of people to marry someone of the same gender, they also make it harder to convert lots more people.

Of course, this doesn't matter: the mark of the true believer is that everything's warped around the central idea. So, for instance, they might say that if someone is so turned off Christianity by its opposition to gay marriage, it's just a sign of how much they need to repent.

For evangelicals who are less sure of themselves, or perhaps more thoughtful, there's an issue, though. Evangelicalism has been tied, in the public mind, to right-wing causes for a good while. And yet it seems that the more headway these causes make, the more atheists they create.

Is it just a matter of sorting the wheat from the chaff, dividing the saved from the unsaved in order to identify the ones who need a bit of work? Perhaps, though the parable of the wheat and the tares, in which it's recognised that grubbing up the weeds might destroy the wheat as well, is also apposite.

More interesting, though, is to ask why people don't like this hard-edged, political religion. And it should be said that this cuts both ways: ministers who stood out against segregation in the civil rights era lost their congregations, too, and it's not difficult to imagine someone in a conservative congregation who came out as a disciple of Tony Campolo having a pretty rough ride.

At one level – the most cynical – it might be argued that people go to church to escape from the world. When they're confronted with the fact that the gospel is a 24/7 enterprise that impacts on every area of life and society, they recoil: it's too demanding.

Or it might be that it's the specific causes associated with the religious right that are so off-putting. Personally kindly people are capable of the most horrendous abuse towards gays in general, or Muslims in general. And that doesn't work: far more of us nowadays know people who are gay. They might be members of our families. They aren't monsters of depravity, they're just folks – and when the religious right tells us otherwise, we don't believe it.

There's probably some truth in each of these answers, depending on the individual concerned. And that's the point: it depends on the individual.

The trouble with political Christianity is that it simplifies orthodoxy to the tiniest possible range of issues. It draws a circle with the righteous on the inside and the lost on the outside – but the only ones on the inside are those who hold the 'right' views about abortion and gay marriage. For people who might be drawn to Christianity but know they don't fit in that circle, there's nowhere else to go but 'none'.

How you feel about that depends on how you feel about these issues. For the average middle-of-the-road evangelical or liberal, it's a crying shame – think of all those people who are put off coming to Jesus by the nastiness of some of his disciples. But that cuts both ways: think of all the people who felt exactly the same when their minister heard a sermon by Jim Wallis and started preaching about social justice.

And perhaps the answer is one that neither camp can feel entirely comfortable with. Taking a stand on political issues – defined as questions of justice that affect the whole of society, not just the church – is never pain-free. It will always exclude and upset people. So the cost has to be counted before it's done. But as well as this: it's possible to hold beliefs with a passion, and to regard them as self-evidently true and righteous, and still to express them with love, patience and generosity towards those who don't share them.

Political Christianity doesn't do this well. It thrives on demonising the enemy. In the US, it has long hitched its wagon to a Republican agenda. Evangelicals are identified with Trumpism, and they may come to regret it.

If we are to be salt and light in the world, it's on the understanding that we're also the light of the world, reflecting the light of Christ. When we let one agenda item crowd all the others out, we fail to present a full, attractive and powerful gospel.

Follow Mark Woods on Twitter: @RevMarkWoods