"Acceptable reason" for what?

The headline and anecdote do not match.

All the Waymo Driver did was pull over and wait for the Support Team and the law enforcement response. It was in a commercial parking lot. It did not "deliver them to the police". It did not lock the doors. The children would have been free to exit after pulling over. The car simply refused to take them all the way to their destination.

Seeing that they were illegally drinking alcohol as underage minors, and illegally targeting innocent bystanders with missiles, what sort of acceptable reason do you need to contact Support, and thereby have law enforcement involved? I think it was a perfectly acceptable reason for the Waymo Driver to refuse service to these customers who had broken their policies.