Why I'm not sold on machine learning in autonomous security

Tell me if you've heard this: there is a new, advanced network intrusion device that uses modern super-smart Machine Learning (ML) to root out known and unknown intrusions. The IDS device is so smart it learns what's normal on your network and not, immediately informing you when it sees an anomaly. Or, maybe it's an intrusion prevention system (IPS) that will then block all malicious traffic. This AI-enabled solution boasts 99% accuracy detecting attacks. Even more, it can detect previously unknown attacks. That's an amazing sales pitch, but can we do it?