What does an antisocial young person look like to you? A sullen boy in a tracksuit loitering in a shopping centre? A hard-faced girl in a fast food restaurant snapchatting selfies? An apple-cheeked choir member doing the hand jive?

That last one maybe seems out of place – and the young people of Prestonwood Baptist Church certainly stood out in Edinburgh on Saturday as they sang, rapped and danced on top of the city's Waverley Mall.

I was in the area searching for marauding youths, after learning that the KFC in South St Andrew Street had turned away unaccompanied under-18s due to ongoing concerns about antisocial behaviour. Clearly the ban is not a blanket one, as groups of young people were merrily consuming pressure-fried chicken in its basement at the weekend, but a marker has been set down.

KFC is within its rights, as is any business, to refuse service to anyone it chooses, and clearly this goes beyond kids flicking French fries and having a carry on. Police Scotland wouldn't have a codenamed operation dedicated to tackling youth disorder around East Princes Street if that were the case. But legal definitions of antisocial behaviour have always been tricky. No behaviour is objectively antisocial: the criminality is in the eye (or ear) of any beholder who is put in a state of “fear or alarm”.

As the number of public spaces open to young people continues to shrink, there's surely a danger that anti-business behaviour – young people being loud, high-spirited and irritating, as young people are often inclined to be – is increasingly conflated with antisocial behaviour that is a genuine menace to society. Any across-the-board bans are liable to foster resentment and frustration, and risk fueling inter-generational tensions.

So what of the happy clappy choristers bringing youthful cheer to battle-scarred Edinburgh? There was nothing frightening or alarming about their slick routines, but by about the second chorus I began to feel a little queasy. Something was amiss here. Who were these implausibly squeaky-clean bunch, and where had they come from?

The answer, of course, was North America: the Prestonwood “megachurch” is based in Texas. How nice that they'd come all the way to Scotland to share the joy and love in their hearts.

Well, not very nice at all, actually. This church ticks every box on the Ugly Religious Fundamentalism checklist: homophobia and transphobia, an obsession with sexual purity, and a firm anti-choice agenda thinly disguised as concern for women's wellbeing. They don't seem too concerned about facts, either – one of the organisers erroneously informed me they'd been granted permission "by the government" to perform just up the road from our parliament.

The church doesn't mince its words when it comes to homosexuality: God doesn't make gay people, so any form of same-sex attraction is merely “confusion” that needs to be cleared up. When it comes to other matters of sexual immorality it's probably best not to ask founding pastor Bill Weber (he bowed out years ago after an extramarital affair), but the basics can be simply explained to teenagers with the aid of a craft project. Why Pursue Purity? involves pinning tatty paper hearts to the fridge as a reminder they'll be permanently soiled if they “give themselves away”.

All of which nonsense becomes deadly serious when a young woman fails to heed the warnings and ends up at Prestonwood Pregnancy Center. In case you're unfamiliar with these kind of facilities, they exist to frighten and manipulate women into ruling out abortion. A hallmark of these dreadful “advice centres” is the provision of early sonograms – just to double-check the result of the pregnancy test, you understand.

If antisocial behaviour is that which seeks to damage and disrupt the tolerance, compassion and respect for human rights that characterise our society, then this organisation surely has the potential to do a great deal more harm than a few dozen delinquent teens getting high and making a nuisance of themselves.

What message does it send when a shopping centre welcomes this kind of musical Trojan horse into a Scottish city, and where do we draw the line? A neo-Nazi puppet show at the Gyle Shopping Centre? Magic tricks by Islamic State at Buchanan Galleries? I'm sure most Scots are far too savvy to be taken in by evangelical showmanship, but that's not really the point. As a nation we should be stating clearly: bigots are not welcome here.

In the meantime, we can deal with problems on our own doorstep by engaging, not demonising; including, not banning. And most importantly, not tarring all teenagers with the same brush.