While Google's self-driving cars are anything but common right now, there's overwhelming evidence to suggest the technology is realistic enough to one day seem safe and suitable to the public satisfaction.
And while the programming and intelligence necessary for a robot to make the walk from its autonomous car to your door while carrying your packages doesn't yet exist, it's far more likely that the engineers and roboticists at work on these types of problems will be able to solve them before
Don't agree? Nevada and Florida already legalized autonomous cars and legislation is underway in Michigan and California (Colorado's proposed legislation wasn't successfully passed). While the legal side of the self-driving car story is already underfoot, commercial drone certification isn't even slated to begin until 2020. Pair this with rapidly developing branches of robotics such as machine learning, and it seems like the robot delivery guy will beat the robot delivery helicopter to your door.
Disclosure: Jeff Bezos is an investor in Business Insider through his personal investment company Bezos Expeditions.