The recent spat between the Pope and Donald Trump is a new twist in the already extraordinary US presidential campaign. But it poses a question as old as religion itself: who is the true “keeper of the flame?”

The Pope’s view is Trump’s plan to build a wall to keep out Mexicans is not one which a true Christian could support. Mr Trump described the Pope’s remarks as “disgraceful”.

There are countless examples from just about every faith of disputes over who is a true believer. This country has its own bloody history of rivalry between Protestants and Catholics. And we are confronted every day with news of atrocities committed by factions in the name of Islam who are denounced as un-Islamic by others of the same faith.

Putting it simply, the Pope says how can building walls to keep out migrants be squared with the Christian principle of loving one’s neighbour? Incidentally, love of our fellow human beings isn’t a peculiarly Christian ideal. Humanists also readily identify with it. The Pope’s intervention does raise uncomfortable questions about the spiritual integrity of our own government members who claim strong Christian values but advocate stricter border controls to keep out people fleeing persecution, war and poverty.

Humanist non-believers don’t form their judgements through the lens of ancient scriptures. A combination of decent human values, common sense and weighing up evidence is at least as good a guide, particularly when trying to address complex modern problems in a world so utterly different from that of biblical times. It is foolish to pretend there are any easy answers to the issue of mass migration. However it doesn’t require the insight of a great religious leader to reach the conclusion that Trump is a thoroughly unpleasant and dangerous demagogue intent on whipping up the worst of human responses. More from Paul