It may be that the relationship was absolutely consensual. And it's a shame that people who work 90 hours a week and pretty much only let their guard down with co-workers can't really let loose.
But we have an emerging consensus (It really is new) that you don't fuck the help, no matter what. Well, I suppose, if if the subordinate said they'd quit because the relationship is more important, maybe that would be an exception, but then would the subordinate actually quit? Should the boss rely on that?
Ignoring the rule, even though not a legal rule for campaigns, was terrible judgment, both on a personal and societal scale. Even if every detail other about the relationship made it seem OK, it wasn't. We can find someone better.
It really is a shame about people whose whole waking time is working, though. I don't know how standards can be tweaked in the years to come to take that into account.