The reality is there are aggressive people in society that have a tendency to escalate things. If police are trained to only de-escalate, it removes a powerful check on aggressive escalation.

The second order effect is an increase in events like people being pushed onto train tracks, glass bottles being thrown if you glance the wrong direction, etc.

I think optimally you have a police force that is trained in de-escalation but also escalates things slightly more than the average citizen and thereby provides a service to society as a buffer.