It's not inherently sexual assault. I never said it was. It is, however inherently a huge conflict of interest, and, depending on the circumstances, is likely to be sexual harassment.

Even if the two people in the relationship are fine with it, and there is no abuse of the manager-subordinate power dynamics, and all the other problems associated with this...

It can create the perception that the reason Sally is getting a good performance review, is because she is sleeping with the boss. This is absolutely toxic to a workplace, and irresponsible of the CEO.