Not sure I agree. Citizens have a right to see the public information posted by their elected officials. But that doesn't mean the elected officials have to provide a billboard for all of their constituents.
Let's say an elected official hung constituent letters outside their office. Would they be obligated to hang every letter received, or could they curate the letters in some way?
What you're suggesting is that the govt should be allowed to only let sycophants post praise, while blocking any criticism or unwelcome comment. Ridiculous.
Every announcement is made in a public square, and once said, every citizen has the right to also shout in that square. The government official is free to cover his ears.