Shari'a courts in New Zealand

I frequently hear people arguing against Muslim immigration as it will lead to Shari'a courts being established in New Zealand.  After all, they say, such courts already operate in parts of the UK and/or Australia.

When such people talk about Shari'a courts, it seems they are thinking of the kind of courts operated by the Taleban or ISIS - courts which hand out sentences such as stoning for adultery.  If that's what comes to mind, I can understand why people don't want that here.

However, is that what really happens in the UK or Australia?  Does a court really sentence a woman to stoning or a man to have his hand cut off and it is done?  I seriously doubt it: those things are serious crimes under UK and Australian law and would certainly attract substantial notice.

Instead, the situation seems to be much more like 1st century Palestine.  Back then, Jesus was tried by a Jewish court and found guilty of crimes deserving execution.  But the Jewish court didn't execute him: they had no authority to do so, and presumably would have faced very serious consequences if they'd tried.  So they turned to the state court (i.e. Pilate, the representative of the Roman government) and tried to convince him that what Jesus had done warranted execution under Roman law.  If they'd failed, Jesus would have stayed alive, regardless of what the Sanhedrin found him guilty of.

So Shari'a courts in the West restrict themselves to family and business disputes, along with providing guidance on religious observance: areas where the secular state is comfortable with allowing them jurisdiction.  Even the Daily Mail, in a 'shocking' article I found, wasn't able to find them acting beyond this.

And isn't that what already happens in New Zealand?  We have church courts - such as the Presbyterian one that tried Lloyd Geering for heresy in the 1960s - but they have pretty limited jurisdiction.  Just yesterday I came across the news that charges have been brought against Jeff Sessions for child abuse (relating to the separating of children from their parents at the US border) - but it's in a Methodist court so, whilst they could presumably excommunicate him if he's found guilty, they can't send him to prison.

I expect we already have such 'Shari'a' courts in New Zealand: individual mosques making decisions about the conduct of their people, collectives of multiple mosques handling more complex or high-profile cases, just like churches do.  They aren't currently part of the formal mediation system as they are in the UK, but I expect they're there.  And I see nothing to fear in them and wish people would stop using them as an argument to prevent certain people from joining our society.