Sorry, I don't quite follow. The entire point of these systems is that it is desirable to MITM your own traffic if you want to insert a security scanning device that can, for example, scan downloads over HTTPS for malware.
Fundamentally, the technique only works with the co-operation of the client, which must recognise the authority used by the certs from the MITM device. From a technical point of view we are therefore assuming the person controlling that client system is in on the arrangement.
Now, we might consider it desirable to warn users of that client device that this is happening for other reasons, if the user is not the same as the person ultimately controlling the system. For example, in the scenario I mentioned before, it might be considered appropriate for the employee to be warned that their "secure" connection to their bank is being affected in this way so they can choose not to continue if they don't want to. But this is getting beyond the realm of technology and into law and ethics. Indeed, if the person controlling the system is hostile and the system can't be trusted, in the end there is nothing technical you can do to safeguard the user anyway.
Fundamentally, the technique only works with the co-operation of the client, which must recognise the authority used by the certs from the MITM device. From a technical point of view we are therefore assuming the person controlling that client system is in on the arrangement.
Now, we might consider it desirable to warn users of that client device that this is happening for other reasons, if the user is not the same as the person ultimately controlling the system. For example, in the scenario I mentioned before, it might be considered appropriate for the employee to be warned that their "secure" connection to their bank is being affected in this way so they can choose not to continue if they don't want to. But this is getting beyond the realm of technology and into law and ethics. Indeed, if the person controlling the system is hostile and the system can't be trusted, in the end there is nothing technical you can do to safeguard the user anyway.