Why would the Brazilian authorities spend any kind of money defending network infrastructure that isn't even in their country? I doubt the sponsors have their stuff hosted in Brazil. What they do have in droves are script kiddies; most of my lastb entries for "root" or generic accounts like "mysql" come from Brazilian IP ranges. So it isn't even as if they're going to get more "hack" traffic than usual.
Most of the World Cup facilities are probably going to fall in disrepair again, that's what happened after the last Brazil World Cup and that's what's probably going to happen again. The media might not be harping on that, but at least one of those stadiums doesn't even have running water. They set up a big-ass tank to be used for the duration of the World Cup, I'm guessing that tank will rarely be used, if at all, after the Cup.
I suspect the reality is these are typical wallflower skiddies that were either too fragile to do sports at school or had no athletic skills. They resent the 'jocks' and their sports and therefore feel the need to throw a tantrum.
Brazil is basically the football country in South America, second closest would be Argentina. Brazilians are protesting the World Cup themselves, which shows it isn't just the "jock haters" who are mad at the event.