It's a sign of our troubled times that we're even talking about the greatest threat to civilisation in everyday conversation.
Some might argue the greatest threat is the twitchy tweeting trigger finger of the leader of the free world. Just this week he tweeted: "Why would Kim Jong-un insult me by calling me 'old', when I would NEVER call him 'short and fat?'"
Sticks and stones and all that, but nuclear weapons probably will hurt you.
Then again, if we survive Trump v Kim perhaps the greatest threat we face is climate change. Though non-believers probably aren't too worried about that.
And that's where celebrity scientist Professor Brian Cox, who was in New Zealand last week, comes in. He is someone who knows a fair bit about the big picture and of anyone he should know where the true threat lies.
When he was asked the question he said the biggest danger to civilisation was in fact the anti-science movement. Or, in his words, anti-vaxxers, climate-change sceptics and the like.
In an era where the world's most important people can yell "Fake news" every time they're called out for unacceptable behaviour, our relationship with the truth is becoming a bit like some of those relationships on Married at First Sight.
There was once an album by the Manic Street Preachers named This is My Truth, Tell Me Yours. It seems these days that if someone else's "truth" doesn't suit your situation - an inconvenient truth, perhaps - you can just come up with one that does.
Except Cox is right. It's a dangerous situation that's getting more dangerous.
Anti-vaxxers spread lies that endanger their children and ours. Climate-change deniers who can't see past the ends of their noses, or wallets, affect public policy with political pressure in ways that will have devastating consequences in years to come. Let's not even start on the fluoride debate.
Why, when we now have the tools to understand the world so much better, are some so wilfully blind, at great expense? Sad!