It's tricky in some situations. Delivery drivers cannot see whether they got a tip or not, so they can't choose whether to serve you or decline, and they end up working for close to nothing. But of course, I blame the food delivery brokers.
This is not true for DoorDash - they can see the tip amount before accepting the order. I think that such a "tip" should not be treated as a tip for tax passthrough purposes - it's a bid for service.
As you should. It's illegal to pay below minimum wage. If they don't get tipped enough to make minimum wage, the employer has to make up the difference. Of course minimum wage needs to be increased but that's another topic.