That sounds really weird to me to bring up, regardless of whether it's true or not. As in this makes sense when you're thinking of trying to hire folks trying to gauge passion as a proxy for their performance when you can't directly observe it, but when they're working for you, you don't need proxies! You can directly observe performance!
So passion seems pretty irrelevant as soon as someone is hired, unless you're afraid of them jumping ship. But that's the nature of the beast. Employers can fire employees and employees can jump ship. Such is life.
> there is nothing "unfair" about employers desiring passionate employees
I'm a bit confused; I mean there's nothing unfair about desires in general? Someone could want a billion dollars to fall from the sky into their lap and I might say "good luck," but there's nothing unfair about it. Employers might desire their employees to want literally zero pay and employees might desire their employers to give literally zero work. Good luck to the both of them.
The question then is not so much desires as it is the actual dynamics of the job itself and to what extent those desires are actually manifested in observable behavior.
I think the overarching theme that the_local_host was bringing up has to do with the language of morality in general.
You can talk about the employee-employer relationship in a very dispassionate sense as one of mutual transactional need with one discarding the other when one is no longer needed, which is fine. You can also talk about the relationship in the language of fairness and passion, which is also fine.
But there's something pretty unsettling about crossing the two together, especially when the perceived dynamic is that when it's convenient for the employer they slip into one or the other rather than when it's convenient for the employee.
EDIT: In response to your additional new line: "I agree that passion shouldn't be a requirement per se (whatever that means) if job performance is otherwise good, but passion is very highly correlated with job performance."
I think the original point of the_local_host's comment is that it's just kind of weird to talk about passion at all or whether an employee "should" do something or not or even the notion of employer/employee entitlement.
Just make the job expectations explicit. If an employer wants employees to work weekends make that explicit in the job description. If the employer wants a work product that a typical employee can only produce after 100 hours of work in a week then fine, ask for it, just make it clear upfront. If the employer wants employees to work extra hours for deadlines, fine just make it explicit.
The employee then takes it or leaves it. And from the employer side either the employee fulfills those expectations or doesn't.
But don't leave it implicit and then complain about the lack of passion, which is what I think the_local_host was pointing out.
(There's wider policy questions of whether you want to incentivize or disincentivize that behavior on a societal level, but that's an altogether different scope/level of conversation.)