Like the trolley problem, outside of a limited group of aficionados, most people don't care about this kind of argument because it's excessively technical and irrelevant to what people care about.
Well, that's not completely true. If you're a union worker, it can be harder for the school to rid itself of the problem employee. Same for many other members of strong unions.
That said, they have to have some process to ensure that unfounded malicious accusations don't both undermine (oh, I hate this phrase) legitimate problems and get innocent people fired, while also ensuring (sexual conduct) violators get their just desserts.
That can make it awkward for a union representative at a disciplinary hearing who is counseling a troublesome employee. Sometimes the lawyer might tell the employee something like, "I can get you off this time but they're gunning for you, so you're better off resigning and taking severance." Which is true as far as it goes, but the lawyer and the union leader are actually thinking, "this guy is an asshole and we need to get rid of him without looking like we sold him down the river."
Long story short: when the employer and union have a good working relationship, a union has no trouble showing a problematic employee the door.
The real issue that I saw repeatedly is that employers will often try to unfairly fire employees, either to circumvent contract rules or because of incompetent or malicious supervisors. They'll even go so far as to concoct complaints out of thin air. In such a hostile environment, when a legitimately problematic employee is under review the union has to take extra care to ensure the legitimacy of the problem. Furthermore, it's more difficult organizationally (i.e. maintaining the trust of union members) to usher a bad employee out the door when N previous employees were screwed by the employer. (Because the details of misbehavior often need to remain private for legal or practical reasons, it's difficult for both employer and union to be transparent with rank-and-file about why an employee needed to go.)
The moral of the story is to maintain a good working relationship. It's ridiculous that employers can't always do that, but I think it speaks to systematic problems in continuity of leadership of large public and private employers. Every successive leader (CEO, Police Chief, whatever) spends a substantial amount of his time attempting to unwind transactions executed by the previous leader, rather than moving forward. That ultimately leads to inconsistent, unfair, and often egregiously improper management practices.
