You’re only thinking of the morality side of it.

It’s also wrong because they work for a company that probably says subordinate-supervisory relationships are forbidden because of the power imbalance and complications around how a personal relationship–or even the perceptions of one-- might affect workplace decisions. Co-workers–even non-supervisory-- who might even be at the same “level” or their work brings them together for anything can be incredibly problematic. All of this is even at a local, department or site level to say nothing of C-level consequences. This also says nothing of the fact that one of them is in charge of the function, HR, who would be the person most responsible for ensuring this kind of conduct didn’t happen between employees. The hypocrisy and abdication of duty couldn’t be more severe. Both have lost all credibility with anyone in their company, which means they cannot lead others.