People don't birth or rebirth often enough for the text to be that big of an issue to the people who have to see them.
As for the privacy thing, I don't think its that big of an issue for people to know when you birth or rebirth. If someone cares enough about the levels of people from guilds and whats going on, they probably wouldn't be that lazy as to not just check the CP.
It may be nice to have the ability to turn off your seeing of those messages, or those messages being broadcast about you, but there are far more important things to be worked on than that.