Absolutely not true as a blanket statement. Maybe if the driver monitoring is so lax that you could conceivably trick the car into poorly driving itself, but the system I use, Comma [1], has incredibly strict driver monitoring.
There is absolutely no doubt I'm a safer driver with Comma than without it. I'm still in control, but Comma not only allows me to expend less effort driving (which allows me to stay alert over longer periods of time), but also be much less emotional when driving. I'm pretty convinced that a large percentage of accidents are caused by frustrated or bored drivers doing crazy things that you just don't feel the urge to do with the assistance of self-driving.