Italians tend to be an uncivil lot. If I were in charge of La Scalla I would have the booers grabbed and booted out of the hall, and never have them allowed back in. You don't like the performance, fine. Just walk out and maybe even ask for a refund.
Oh no..... this is part of the charm of the Italian opera experience, doncha know. It's part and parcel of the traditional La Scala performances to boo an underperforming singer!!! ;-)