Yes... for certain values of A and B. If you're delivering to a business in a building with a helicopter port. Delivering to a front porch is entirely different. Then there's the matter of how many will be in the air... maybe Amazon only has a few for "important" immediate deliveries that people are paying a lot extra for, but then if Amazon does it, how many other companies will be allowed to do it?
How many drones can you allow in the air? Like segways... might be OK if a few people used them, but if everybody did, then it could be really bad.
What happens when a motor fails? When a wind gust between buildings causes one to smash into the side of a building? When it crashes into heavy traffic (automotive, pedestrian, or otherwise)?
I'm a big fan of the Golden Rule ("Do unto others..."), but, to me, a corollary is also "What if everybody did it?" That's the question, IMO.