The quote above is from the lecture Roy gives the Doctor, just after Guido has blown himself (and a bunch of invading vampire fish aliens) to smithereens. It's got echoes of Davros' speech from Journey's End, where he points out how the Doctor's companions don't return to a normal life, but continue fighting. Amusingly inverted a short while later when Roy refuses to leave the Doctor.
One thing that bugs me - the perception filter. Amy damages it, which causes it to occasionally fail. But why would that prevent her turning the filter off? And why does she even need to turn it off? It's a perception filter, not an actual shape-changer like the Slitheen suits. The in-universe explanation for perception filters is that they're not invisibility cloaks, they're not shape-shifters, they just make you not get noticed. They don't work on alert people who are expecting to see the real thing, and they don't work if the cloaked person tries to get noticed. So surely, the fish-aliens would see the real Rosanna and not eat her?
I don't recall seeing a crack in this episode, but the silence at the end cannot be a good sign. Didn't Rosanna say something about running away from the silence?