People band together? Yeah, criminals band together. After every major hurricane there is looting, just sometimes it is more widespread than others. Remember 9 years ago hurricane katrina? There was no law and order for just a couple of days and new orleans became a complete shit show. Criminals actually thought it was their city to keep. There was looting, murder, rape. Bodies were left on sidewalks/the road. Buildings were burned down. They were unable to evacuate ppl from charity hospital because criminals were firing at the helicopter for no reason other than they could because they thought the city was theirs to keep.
There is a vast difference between something like a tornado, or an attack on a very small area like 9/11, which typically only effects a very small community so the community around it pulls together; law and order is left unaffected. Those are in no way comparable to something like a hurricane katrina or, in the case of twd, a zombie apocalypse, which has left society with no law enforcement for 18 months and seemingly no return to law and order, ever. If you don't think the world would be at least just as brutal as it is in twd then you have put too much faith in humanity.