one of PM usage will be for the marketplace
because PM+Escrow = ability to start one..

For me it's not acceptable to send only message that we "could not regret later on"
it can sometimes involve ur personal data/information that you need to send to someone.
It can be encrypted, but also deleted if or once you decide its not useful to have it on database anymore.
still have mixed feelings on this ;) but i totally hear ur solutions as well