Arguably no, it's not. This is why Waymo stopped working on level 3 and switched to level 4/5 systems. It's also why most vehicle manufacturers up until now have only supplied ADAS features which provide backup to the human driver (lane departure warnings, emergency braking assistance etc.) rather than features which drive while using the human driver as backup.

There are a few coming out soon (SuperCruise, Pro Pilot) that will offer some degree of level 2/3 operation. It'll be very interesting to see how that goes liability-wise.

Not if it requires constant supervision, yet lulls the driver into a false sense of security such that they are predisposed to not provide that constant supervision.