When the game was first released, the sector AI didn't enslave or emancipate. And people complained. And so they changed it. And still people are unhappy.
I wouldn't call this "inexcusable." I'd say people should be careful what they ask for.
I don't think that's the issue here. The central problem is that the devs have introduced two features in this game -- slavery and AI sector management -- without proper design and testing to make the two ideas compatible.
It's reasonable for players to want the sector AI to manage slaves in some situations, like if you're running a "soft slavery" style of empire. It's also reasonable to want the opposite in other situations where slavery is total and emancipation doesn't exist (you're role-playing the Kzin).
All it needs is a setting labeled "Sector AI allowed to enslave and emancipate?" in the setup menus.
And if the devs can't manage that, then the default should be to stop the AI from managing slaves as the default setting, because it causes the least damage to slave-owning empire management. Right now, a slaver empire is literally unmanageable unless you mod out sectors completely.