When you talk with a friend in the street, people around could be listening to your conversation. So it's a public place.
I think, that the public IRC channel and the real street are quite different things.
Even in the SL world streets look more like real, there is communication distance.
On IRC you always know a number of persons who can see your public messages.
People should behave accordingly and responsibly!.. Or just use private messages.
And yet, would you agree if governments woud decide to put mics everywhere in the street, so that all "public" conversations would be recorded and archived ??
I can not be sure that this is not happening now.