It's much harder to hit something in the air.

As any pilot knows, the stomach unfriendly words from Tower are: "Caution, Wake Turbulence".

The air, being a sparse fluid, can change fast. Especially so if another aircraft has flown through it recently. It's not that there isn't anyone there, it's the air they left behind is all non-laminar now. Doubly being suddenly downwind of stationary objects like towers, wind farms, and mountains.

Also, quick point of caution: One reason early flyers died a lot because they flew so low. Even after a few meters of height, just about any crash is likely to be deadly. Paradoxically, the higher you fly, the better off you are (in certain cases). In flying, your height can be measured in 'mistake recovery time'. The higher you are, the more time you have before you hit the ground, the more time you have to fix a mistake. If your engine cuts out, you have a longer glide time to look for a lake. You can get a fuel pump restarted or unfrozen. You have more time to grab a parachute and bail. Etc. It took a long time and a lot of lives to realize this. As such, personal drone-choppers will be more dangerous and I fear we will have to re-learn the lesson of height being a friend in aviation.

It comes with a parachute

If anything, that makes it more dangerous. Besides a sense of 'false' security, chutes do take a certain amount of height to catch air and become safe. IIRC it's about 100m and turbulence will affect that in strange ways.

In the end, I still fear tech like this will not be as stringent as needed.

Which doesn't help at all when you hit wake on final. Chutes take a surprisingly long time to grab the air and slow you down.

But much easier to hit something on the ground (powerlines, houses, highways).

It's much easier to be cocky and negligent if the last 100 times you drove you never encountered something to hit.

Don't today's drones and airplanes demonstrate that automating flying is a lot easier than automating driving?

I work in the field. Basically, yes. On average it is easier to fly than it is to drive, mostly because there's far fewer things to crash into. But on the other hand, almost any failure can become catastrophic - falling out of the sky will usually have much worse consequences than, say, bumping into the car in front of you.

That might stop being true if the air is as crowded as the roads.

As long as they're all outfitted with transponders, and piloting is automated, I don't see that being an issue.

The air won't have pedestrians and bikes!

Para/hang-gliders, small drones, birds. There's plenty of stuff you don't want to hit :-)

Cue legislation to make kites, balloons and RC aircraft illegal

No they don't. Drones are generally only allowed to fly at very low altitude in most US airspace because they can't reliably see and avoid manned aircraft operating under VFR.

True. But there is a reason pilots are still a requirement.