Extreme labor inefficiency. Today Amazon's driver can deliver an order of magnitude more packages than a person with a wheel barrow could. There are 100,000+ Amazon drivers in the US. You'd need at least 1,000,000 people with wheel barrows.
That's true if we decide it's a good idea to continue to deliver millions of packages of small plastic goods every day. A big part of that is probably also due to the USA's massively isolating suburb design and poorly layed out roads.
I think in aggregate Amazon does more harm to our society than adds value. Its "value add" and service requires the degeneration of labor rights, a massive carbon footprint, and unethical shadow-UX practices on its own website.