General audiences have been believing that the messages spread by mainstream media are true for many decades now. And of course the media shapes the mind of the audience even if the messages are not taken at face value. But changing "all the media" equals changing the whole system, because the media work along with the tendencies of the system, or right away serve the system.
So yes, if we could replace all the content of the mainstream media towards promoting peace, love, sustainability, unity, etc., that would of course have an effect in the global mentality. But the plan goes inside of the idealist bag of candy, like suggesting to cut off the world military expense for a week in order to solve world hunger.
To change the media you need to change who owns the media and their reasons. Probably by the time that was done, the role of the media would not be a pressing concern.