Perhaps “Get off of Earth before Nemesis sends some more comets our way”
Nemesis: http://en.wikipedia.org/wiki/Nemesis_%28star%29
Reasoning: The Roman invasion could have been predicted, but wouldn’t have been well supported by evidence—although foreign invasions were certainly a repeated (even cyclic) phenomenon. Of course, the Nemesis hypothesis rests on an unproven root cause of all major extinction events, whereas invasions came from various, known causes...
I’ve done this occasionally, actually.
One time, I found a very opinionated guy with a high opinion of himself—I think he might have been Objectivist, but he scoffed at literally every philosophy he mentioned so it’s hard to tell. I figured that trying to debate him would just end the conversation early; he’s the type to quickly classify those who disagree as sheeple. So, I copied his conversational style a bit, agreed with him on most points but disagreed enough to keep the conversation interesting and get some insight into his views. I don’t think I was directly dishonest about my opinions; I just positioned myself as an ally (in an “Us vs. Them” sense) and worked from there.
I recommend this to anyone who wants to understand the reasoning of, say, creationists, but can’t talk to them without reaching an impasse of rationality vs. dogma.