I think it's pretty clear to see that this role has problems of compatibility, and is compromised, with the public knowledge of her former porn star career. Unfortunate, but this is the simple facts of the situation.
Most of what you're saying about the necessary attributes of an effective teacher are true. However the problem is the statements like this. You're basically setting forth the argument that "Ms. Halas is a former porn actress, and a porn actress would create distraction amongst middle school students, therefore she cannot do her job". You've yet to actually describe why she can't do her job because of her history (Or even why a teacher can't deal with distraction in general). It's not as if a single distraction opens forth the gates of hell and the children turn into soulless demon beasts of Satan, intent on never listening to anyone with authority (Although some truly do believe of that of children).
There are a couple of different dynamics at play here.
1. The age of the students being taught.
The problem with having a former porn star teach middle school children is that it's an attraction to an activity that is illegal for children that age. Every porn site has 18+ written all over it (21+ in some jurisdictions). Children will obviously ignore it because they want to see Tiffany Six get sexed, and the particularly cruel/spoiled ones will add the vid to their smartphone and play it in class, among a million other potential distractions. The parents are also right to be concerned because some may not even want the topic brought up in class to begin with, and Ms. Halas's history makes that impossible.
An attraction to an activity that's illegal for children of that age? No more so than seeing a parent smoke cigarettes or drink alcohol. A million other potential distractions? Distractions in a classroom are not a rarity, and the certainly do not mean chaos. Part of a teacher's job is mitigating distractions. Such actions that you described would be swiftly dealt with by the teacher.
And while I can understand the sentiment of parents not wanting information like that being brought up in class when they don't want it to, I'd also have to take the standpoint of 'When does information like this EVER come up at the time the parents wanted it to?' And nor does the possibility of the subject being brought up by fellow students merit the removal of a teacher.
2. The act itself.
Let's be clear here. "Sex work"/Porn isn't empowering, uplifting, liberating, meaningful, or any of that other PC academic-course-requirement-filler bullshit. It's filling a market demand primarily driven by horny adult men to see as much of their desired fetish fuel as possible. Putting your body up on display for the titillation of others is a base activity designed to stimulate the most primal urges of the human race to mate. It is not therefore not without personal risk or social implication, and in a perfect world the demand for it would be less - the problem is it's addicting for both the consumer and the producer because it works off that primal impulse, and because there is enough money to be made on it in certain realms - thus the sex trafficking circuit. It is a legal activity and should remain so despite the people who abuse it and the people who have problems because of it, but that does not mean it is a positive or wholesome activity.
Let's be clearer here. Hunger too, is a primal urge of a baser form of our beings. Yet we do not frown upon cooks, who take up the profession of creating foods for the titillation of these desires. Baser instincts do not imply immorality. Nor is the arbitrary immorality of an act a justifiable excuse to terminate someone's employment.
Middle Schoolers are in the first phase of dealing with that impulse, and unfortunately it would be just like trying to have Barney the Dinosaur teach a classroom full of elementary school children - they will all fixate on "OMG BARNEY!" and forget about actual learning. Parents will complain that a 7 foot tall purple dinosaur is not a realistic role model for elementary school children to emulate.
This amused me because Barney as a character is fundamentally designed to be a role model for children, so a complete and disastrous failure of an analogy here.
My suggestion at this point is to stop trying to just use (poor) analogies to demonstrate why you feel she's limited in her capacity to effectively teach, and try explicitly outlining the reasons.
As far as Ms. Halas, my recommendation is she try and go for higher Ed. Middle Schoolers don't care about disrupting class and suffer no real consequences for doing so. College students that openly mock and damage their professors can be punished with real world consequences that will actually resonate. Her actions have consequences for her present employment, and that's just the way reality is. She chose an adult activity as her financial means in her earlier life, so her access to children is now limited.
Fundamental misunderstanding of education, here. Teachers who teach at the k-12 level need a degree in Teaching. Professors at a university do not, and have a much different set of requirements for employment. I cannot speak for Ms. Halas personally of course, so I cannot be certain she's precluded from such an occupation, but I will say that the majority of k-12 Teachers are not qualified to teach at the University level.
As for the way reality is, that's really the point here. Just because reality plays out this way, does not mean that this way is the correct way.
There are no conflicting rights here. Ms. Halas does not have a right to teach middle school, just as the kids don't have a right to have their class free of former porn stars as teachers.
This is not the place for a moralistic Aesop about society and protecting rights. A right is not synonymous with "what I think is right." Rights have a specific definition and specific boundaries. They aren't in play here - not in the slightest. Ms. Halas has not been forcibly barred by government authorities from teaching anywhere in the abstract (which, in the absence of an actual crime would be a violation of her liberty) - this school system as decided they do not want to incur the potential negative publicity and other issues associated with her continued employment. Nothing more, nothing less.
You're correct in your assessment that this issue is not "Teacher vs Student" rights. It's actually about the Employee's right to not be terminated from their position without justified cause. Being a former porn actress is not justifiable cause. Neither is general unrest amongst the parents of the area a justifiable cause for termination of employment.
In other words, "You've done nothing wrong on the job, but your existence is irksome and bothers some people, so I'm going to fire you" is said in no legitimate workplace, ever.
There is a reason that the court and school used words and phrases that stated that she was
incapable of doing her job, because that's the only way they can actually get away with firing her.
