Anti-Americanism in Italy has a long, undistinguished tradition. It has historically been present both on the far end of the political left and right, both of which have been very strong in the country in the last century. The Vatican itself is often anti-American. This is a part of its traditional role of opposing secular power, and since we are the secular power now, it sends us oblique messages deploring our wealth and military might. Among other things.
The phenomenon is somewhat more subtle than in other countries. This is also due, I think, to the fact that Italy has a long, long history of foreign occupation by just about everyone, to which they have more or less adapted. Note the proverb: Francia o Spagna, basta che se magna (France or Spain, as long as we can eat). And the Pax Americana has definitely allowed them to eat more and better than in the bad old pellagra days. Further, not to be sentimental, but the relatively recent immigration patterns from Italy to the US ensure that many have a "zio d'America" (American uncle). Much harder to hate your own flesh and blood, at least in a wholehearted and not ambivalent way.
What this means to you, as a prospective American tourist, is that you are not going to be subjected to the frontal onslaught. But as a concomitant of their old civilization and the need to co-exist with foreigners, not to mention the very large role tourism and exports play in the economy, they have developed a good deal of duplicity in this (as in so many other areas). As an American who is half-Italian, speaks Italian without an accent and looks Italian, I can tell you that what many Italians think about America is not very pretty. More on this later.
(above right, truculent, tattooed type with sign saying in the dialect of Vicenza: Americans, you're only good at damage)
