Perhaps Ultron is talking about the act of projection...how sometimes we dislike in others the very things we actually dislike in ourselves. If we're lying about something, we're more inclined to assume other people are lying to us. If we're angry about a situation, it's not uncommon to redirect that anger elsewhere. Could this be what Ultron is talking about?
Maybe he's referencing the fact that, sometimes, we become so reactionary that we actually cause more harm than good. In teaching, we seem to do this all the time. A traditional "lecture and quiz" method doesn't work, so we shift entirely to student-centered and self-paced courses...which fails as well, so we quickly flip back. It seems like teachers (and more realistically, state and local school administrations) do this all the time. As much as we try to manipulate a perfect system, we end up creating a flawed system we later have to undo. Maybe Ultron is referencing the overburdened bureaucracy of society.
It could be that Ultron is simply warning us that there really aren't any monsters in the world...but that people are just as dangerous as the monsters in the old stories. In Beowulf or The Hobbit, the hero had to contend with monsters and creatures, but by the time King Arthur and Macbeth rolled around, the villain wasn't an external force, but an awakened evil within the heroes. Intentionally or not, the lead characters in those stories destroy themselves by acting too swiftly to achieve their goals. In doing so, they allow the very things they feared (destruction of their kingdoms) free reign.
Of course, all of this might just be a movie trailer. Sometimes lines don't make a lot of sense. Nevertheless, Ultron has my attention. By May 1, he'll be all anyone is talking about...