> If two people want to have a private conversation
You response is based on a false fact: that anything you use official company communication channels for should be considered private.
HR functions can and will access such communication to investigate complaints about behaviour and similar. Compliance and legal functions can and will access such communication to investigate complaints relevant to them. They can, will, and often must provide access to such communication to relevant external bodies (legal authorities, regulators) under some circumstances too. Heck, in some regulated environments compliance functions are required not just to view your communications for specific reasons but to actively monitor them for certain activity (if they fail to do so they could be liable for punishments for a due diligence failing). For instance our email is monitored to block distribution of client data, accidental or otherwise.
If you want a private conversation, use a truly private channel not an employer provided/related one.
> they'll just find another means by which to do it
The fact that people will find away around rules, restrictions, and monitoring, is not a good reason for not implementing such rules, restrictions, and monitoring in the first place.
If the private conversation is in no way a problem then, well, there isn't a problem.
If it is something that would cause the participants trouble if performed over an official channel then when/if the matter does come to light it shows malice of forethought and planning (i.e. that the participants knew they were in the wrong and took specific action to hide their behaviour rather than correct it).
> I would quit a job
In many (most?) industries you would not even get a job without explicitly agreeing to the fact that your communications using employer provided/related services can be accessed by some functions of the organisation and distributed to external authorities, so you would not be in a position to need to quit.
That is only according to some law systems though. It does not work like that at all in many European countries. For instance in France the employer cannot read any private conversation (mail/message) of the employee, even when using work email. And no internal rule can change that (it is a criminal offense). If the employer suspects a leak of information by the employee, they can read the message in presence of the employee and a union member, and only in those circumstances.
> If the employer suspects a leak of information by the employee
or if they suspect any other illegal activity.
Even in EU countries where arbitrary inspection/monitoring is not permitted wholesale, there are exceptions where regulatory or other legal requirements trump privacy. Though often there needs to be sufficient suspicion of something worth looking for, I still wouldn't count that as a truly private channel (nor would I expect my employer to provide me with one).
But as I said even in those cases the employee needs to be present when the employer accesses private messages, in addition to a union member. So as an employer you cannot just sneak in and check what has been said, it has to be public. Which I think greatly mitigates the risk. It is not a secret conversation like you would have between lawyer and client but it is rather private.
You response is based on a false fact: that anything you use official company communication channels for should be considered private.
HR functions can and will access such communication to investigate complaints about behaviour and similar. Compliance and legal functions can and will access such communication to investigate complaints relevant to them. They can, will, and often must provide access to such communication to relevant external bodies (legal authorities, regulators) under some circumstances too. Heck, in some regulated environments compliance functions are required not just to view your communications for specific reasons but to actively monitor them for certain activity (if they fail to do so they could be liable for punishments for a due diligence failing). For instance our email is monitored to block distribution of client data, accidental or otherwise.
If you want a private conversation, use a truly private channel not an employer provided/related one.
> they'll just find another means by which to do it
The fact that people will find away around rules, restrictions, and monitoring, is not a good reason for not implementing such rules, restrictions, and monitoring in the first place.
If the private conversation is in no way a problem then, well, there isn't a problem.
If it is something that would cause the participants trouble if performed over an official channel then when/if the matter does come to light it shows malice of forethought and planning (i.e. that the participants knew they were in the wrong and took specific action to hide their behaviour rather than correct it).
> I would quit a job
In many (most?) industries you would not even get a job without explicitly agreeing to the fact that your communications using employer provided/related services can be accessed by some functions of the organisation and distributed to external authorities, so you would not be in a position to need to quit.