What if Anonymous Attacked City Infrastructures and Power Grids?

More importantly, why? If governments are doing their jobs and serving whom they are meant to serve, people as a collective group are well cared for and have no reason to do such harm to themselves. The few who would threaten it are the odd pathogen, quickly and easily dealt with.

OTOH I can see people as a collective group deciding they don't need large corporations like Bayer killing their bees, Monsanto poisoning their food, Visa and MC ripping them off and suppressing speech of those they don't like, etc. But are any of those essential and vital? Perhaps these are more like a cancer that should be removed from the body politic.

TL;DR Anonymous doesn't shit where Anonymous eats.

Then it would be classified as terrorism.