The fundamental issue is one of audience. You always have an audience in any writing, and with healthcare notes this is especially true. The problem arises when you try to deny this, and in the process make everyone your audience, as what writing you need for one reader is very different from the writing you need for another reader.
In psychiatry this is especially problematic because you're essentially always trying to maintain rapport and a relationship with a client, and there are times when the most tactful and therapeutic thing to do is to withhold information at a moment, or even more often, present that information in a very specific way. The way you communicate with a patient is part of your job. You wouldn't behave toward a colleague in the same way you would a patient, but that's essentially what you're asked to do with open notes.
I can imagine the criticisms this might invite — that what I'm saying is an example of how patronizing psychiatry can be at times — but I think there's no way around this. I highly doubt you want your therapist talking to you like you like they would a close friend or colleague, for example, and no professional therapist would do that.
Open notes are this sort of weird wormhole through the provider-patient relationship boundaries that typically exist, and in my experience they just lead to this odd coded language in notes, or pushing discussions offline into verbal discussions between colleagues, or something.
I do think patient records should be available to them, but I agree with others that it might be better to have certain levels of firewall for different types of notes. Some a patient might get immediately; others they might have to make a request for, or something.
It's a difficult needle to thread, but I'm not sure radical record transparency always everywhere is quite optimal.