I don't think it's likely that a bunch of extremists will take over and come after us to exterminate us, and even if they do, I think there'll be enough warning.
The rise of the Nazis was caused by a number of unusual factors, not least of which was the massive economic crisis in Germany following the Wall Street Crash. AFAIK, no other country affected by the recession took such a course. I don't think capitalism is going to crash like that again until it's engulfed the whole planet and has nowhere else to expand into, and it'll take them some time to convert the Islamic nations, for a start.
Even if we do get a massive recession leading to an extremist government, they might not do eugenics. More importantly, there should be plenty of warning. Nothing like it had happened before in the "civilised" world, yet Freud saw the writing on the wall in time to jump ship. Just set aside the price of a plane ticket to somewhere nice while things are still normal. I'm more concerned about starving to death when capitalism finally collapses, but I think I'll die of old age before then.