Twitter is the medium about what's happening RIGHT NOW. In before you would open the TV or the radio to get information about what's happening right now but these days many people would look at Titter to get information about "RIGHT NOW". It could be mundane things about the lives of other people or it could be an event that's affecting large number of people. If something is happening, there would be reports of observations and there would be statements from people in position of making statements.
I don't really think that a state should run a service about what's happening right now but I think that Twitter is invaluable service to the public that needs to be dealt with carefully.
Twitter's power is well beyond the power of displaying ads to users and the only failing thing is the business of displaying ads to users in exchange for money. Twitter's core function is strong, it's not a failing product.