This is more true than it can seem at first. For the GP's point, adaptive cruise behind a car slowing to turn can cause unexpected braking and startle drivers.
Adaptive cruise around sharp corners exposes the current limits of self-driving car vision. These systems usually have a cone of vision in front of the car, that only sees stuff moving 25+ mph in the same direction. Once a leading car is too far around a curve, the adaptive cruise can lose track of the leading car and accelerate sharply.
Some adaptive cruise systems intentionally don't accelerate while on curves, likely for this reason.
Later, when I was pulling into a left-turn lane and thought he was gone on his way, this asshole intentionally cut right in front of me.
If the adaptive cruise control is staying far enough away that it can always stop that is an entirely different problem. Leaving so much distance, so much empty road, between cars reduces the total carrying capacity of the lane, which isn't good for anyone.
Sounds like you are also trusting that car. Would this system follow a car into a dangerous situation? I ran into this sometimes while riding sportbikes. Some car would be following us on a strait, a passing lane, but come the first turn it was way out of its league. I saw more than a couple sliding sideways in my mirror.
This doesn't have to involve speeding. On a mountain highway (BC) fast straits often end in very tight corners. The speed limit doesn't change. Braking, merging and cornering all have to happen simultaneously. Leading bikes in a group will sometimes even accelerate into corners to create space for those behind to maneuver. Any car setting its speed according to the bikes ahead of it is in for a nasty surprise.