Last I might say on this cause I dont want it to be a distraction for the town...but we obviously dont know what the dream did for the mafia. It did something. They got to choose it! They would know that the town could talk at night, and got something because of this if I am interpreting it correctly.
I am assuming the everyone can post at night was obviously not the only thing they got out of it, otherwise why would they choose it? They probably didnt assume people would role reveal cop O_O. I dont think this would be chosen as the only benefit of the dream, unless they had X amount of options and had to choose this one early on to save more powerful ones later on?
This is wild speculation, but, seriously...
I dont think it is far fetched to think that to have this be the dream option that someone wouldnt be allowed to post. It would be a major downside to the dream, yes, but arent the dreams without some sort of negative consequence insanely OP?