There's a tricky balancing act here. I agree in general that it's good to not air dirty laundry and I personally would be very unlikely to publicly write something like this about a previous coworker.

At the same time not sharing information widely about a toxic member of your community can create a "missing stair"[0] effect where those with inside info know to steer away from the person. Meanwhile, newcomers to the community don't have that knowledge and end up getting burned.

I don't think there's any perfect solution here. We each have to judge for ourselves where to draw the line between public shaming and the duty to protect others from potential harm.

[0]: https://en.wikipedia.org/wiki/Missing_stair

It might give somebody enough information to decide not to work for that CEO.

If there's no public acknowledgement that the CEO ran an awful workplace, there's not much to stop him doing it again with another company.