What else should I have done? Just let the kid take the next guys phone?
If I’d called the police, they’d almost certainly have told me on the phone to let the shouting kid go. There would have been zero consequences for him, and possibly some for me.
I genuinely did that kid a favour.
Looks to me like you should be pissed off at the police in your locale for forcing you to fend for yourself against criminals.
The former is just maintenance of basic civic standards.
I'm not even too inclined to blame government, as I consider this minor loss of security a perfectly acceptable tradeoff in return for their economically beneficial pro-immigration policies.
This is just what living in a big city is like, unless you're in a police state.
And what does immigration have to do with any of this?
Yes; under those conditions vigilante justice is a reasonable way to 1) protect society from criminals, and 2) encourage the state to correct its failures of policing.