An 8,000lb van will be using fossil fuels and emit particulates from tire and brake dust. Unless it was incredibly efficient and electricity for the drones was coming from coal plants, the van would emit more pollution.

But the biggest harm is people getting hit by vehicles. Delivery drones are much smaller and don't spend nearly as much time near people. Since drones can deliver stuff more quickly than large vans, they also substitute for individuals driving to a store to pick something up. So the total risk to pedestrians is even less than you might expect from eliminating many van deliveries.