In short: They're still bad for you. They're much better than sugar for you. They mostly don't have any calories and are not digestible carbohydrates. They probably don't cause cancer if used in moderation.
Fun fact: I've sustained high ketone levels while consuming coke zero freely.
This
Also word from Dr Mike https://youtu.be/TguFyTJkLKk?si=Fz8W6Daleb0bXyBL