So through a variety of work-related drama that really doesn't matter, my direct manager's position has opened up. I've essentially been doing the job but without the title for a fair bit of time so I decided I might as well try to get the position officially. I later found out that the position I applied for isn't actually a union position and it's kinda made me start rethinking things, as far as I'm aware it shouldn't actually affect the benefits or hours, just a non-union unit manager position.
Managers are expected to do this when the time comes, but most parts of most management jobs aren't this. Hiring, training, scheduling, resolving (preferably foreseeing) issues, evaluation -- all of this stuff happens in workplaces in AES states, too. Having a manager who at least tries to do those things competently and fairly can be a huge plus for the day-to-day lives of workers.
As for what one does when the bosses call on you to enforce their will? First, you can use your position to frustrate that will, as @CyberSyndicalist@hexbear.net points out. Second, maybe you have to make them fire you at some point -- everyone should have lines they won't cross.
Fully horizontal workplaces can work in some industries, but others (classically, a ship) really do need some people to make decisions and others to follow them. I'd rather look at ideas like democratizing workplaces and electing managers than take the line that managers (even ones chosen by workers) just aren't necessary.