Conversations are repeated every day and this is normal. Sending a PM is not unlike having a conversation with a friend in your house. Either party is able to repeat what us said as they wish and either party has the right to do so.
What about cutting out vital context and then pretending you never received it? You seem to trust people who do that.
I'm questioning kzv's judgement here. Tag Lauda for posting everything with no malicious intent, but don't tag someone who cherry picked words to attack someone maliciously?
Both parties have the opportunity to publish what they wish.
I also dont see much difference between quoting a PM to send to a third party and posting it in public. In both cases, the message gets repeated.