surely you can list the differences between a romantic / physical relationship and a purely platonic one and understand why it is bad when it comes to imbalances in power right?
Unequal treatment in the workplace due to friendship is far, far, FAR more common than due to romance. In fact, I'm not sure I've ever worked at a company of more than a few people where it didn't happen.
yeah, it's one of those things that is really hard to avoid as a manager. Naturally you like some people and don't like others. Maintaining objectivity and evaluating people on their performance despite your feelings about their personality is hard.
This is why good managers don't aim to be friends with the people they manage. You may end up being friends because of team camaraderie and the amount of time you spend in the same building, but deliberately choosing to socialise with some (but not all) of the team is a bad idea.
And exactly the same thing happens if there is a perceived friendship in the team. Was the employee promoted because of their skills or because they're mates with the boss? Were they not promoted because the boss didn't want to be seen to be promoting a friend? Did they get into that argument because they're a brown-nosing jerk that thinks they're untouchable because they go for beers with the boss every Friday?
Both kinds of relationships can lead to power imbalances though. There's nothing special about a romantic/physical relationship in that regard. One can promote their (same sex, platonic) buddy for being their buddy, just as easily as they can promote their girlfriend/boyfriend.