I'll play a little devils advocate.
.....This would allow sellers/buyers to identify themselves and would potentially remove the mutual trust issue (since Bitcoin is anonymous in the first place).
I thought one of the fundamental principles behind Bitcoin was the anonymous nature of it. You even say it!
The protection is there because if USD is not sent to the transaction ID within, say, 24 hours, the BTC would automatically get refunded to the sender.
This sounds like the definition of an escrow service.