If you take into account that most of the people sitting on the floor of the square bought their beers in the convenience store and probably paid less than one Euro for each of them, I don't think that the state will loose a massive amount of income via taxes.
On the other hand, I know that measuring everything by the economical peformance is a really common thing to do in the other side of the Atlantic, but the neigbours have the right to be able to sleep, even with the windows open. Those squares are not zoned as industrial area, so they are meant to be silent at night. By law.
Could there be other problems with everyone using air conditioning all the time?
Windows don’t need to be shut all the time. Just when I’m sleeping, or want some quiet. (I don’t live in an acoustically-isolated environment, either.)
(That said, I and most people I know in Manhattan run air conditioners more or less constantly, while we are in the apartment, all summer.)
Modern technology allows for acoustically isolating virtually any kind of housing. (Provided the windows are shut.) Acoustic retrofitting is expensive, but so is losing the tax revenue from a vibrant public space. A better solution would have involved reducing noise levels inside residents’ homes without smothering the plaza.
(Reminds me of a poster I saw at a club, once. Paraphrasing, “Al sees apartment. Al sees club. Al rents apartment. Al spends all his free time making noise complaints. Don’t be Al.”)