Another Holocaust. Faced with catastrophe, could we become mass killers again?

We never stopped being mass killers. And I doubt we ever will stop being mass killers. One direct consequence of say establishing a permanent colony on some other planet is that eventually we'll have interplanetary war, it's pretty much inevitable that such a colony would sooner or later decide to become autonomous rather than be ruled from earth.

The Dutch have the questionable honor of inventing mass murder (we once flooded a large area of land to drown many thousands of invaders) and we're normally speaking pretty meek. There's a killer in all of us and we exist in large numbers, some of us are more pre-disposed to killing than others and some of us are more than willing to follow orders, no matter how wrong. So, yes, we can and we probably will.

> Hitler described humans as members of races doomed to eternal and bloody struggle among themselves for finite resources.

Hitler was self referential in that sense, he described himself and as long as we have 'little Hitlers' walking around this will continue.