So, after shooting someone on Tuesday night, Christchurch police have decided unilaterally to carry guns at all times until further notice. And in doing so, they've done something which is both dangerous, and utterly corrosive of public trust.
In New Zealand, policing is nominally based on the Peelian Principles and the idea of "policing by consent" - broadly, that the police rely on public consent and cooperation to do their jobs. They win and maintain this consent and cooperation by demonstrating impartiality, using minimum force, and respecting the limits of their power. But guns change all that. They dramatically increase the consequences of police intervention, while changing the relationship with the public from one of trust to one of fear. And that in turn reduces public cooperation. Some people will be reluctant to report crime or provide information when the consequences may very well be someone getting shot and killed. Some will simply refuse to talk with an officer carrying a weapon under any circumstances. They don't even have to wave them around - its just that people carrying guns are automatically threatening, and people will avoid them.
We know our police are racist: their own use-of-force reports show they are six times more likely to beat a Maori than a Pakeha, and ten times more likely to pull a gun on them. We know they regularly use inappropriate force - you just have to skim the IPCA reports to see that. We know they're ill-disciplined and don't care who they kill - their mad dog approach to police chases shows that. And all of this suggests that routinely arming them will inevitably lead to them threatening and shooting people with guns. And that makes them not protectors, but a threat to public safety.