Update (Sept 6, 2017). I’m adding this CBS video about cooperation and finding commonality during Hurricane Harvey. “No one cares about the color or creed of their rescuer.”
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One of humanity’s greatest assets as a species is our flexibility. We can live in a range of environments, and adjust to new social realities, diets, technologies, ideas, languages, etc. Our kids live in a world where communication across the globe is instantaneous, something that our ancestors would never have thought imaginable. Yet it’s completely normal for this generation. We adjust.
Still, nothing is cost-free. One drawback of our incredible plasticity and ability to hold a multitude of beliefs is an inherent risk for conflict. I say “avocado.” You say “mango.” People disagree on just about everything. What should we have for dinner? Are other people fully human? How should taxes be spent? Should baby boys wear pink? Are Nazis bad? Are there hats?
(Answers: (1) whatever you want; (2); YES!; (3) it’s up for debate; (4) it’s culturally malleable; (5) YES!; (6) obviously).
Is there anything that people might agree on? I had hopes that people could come together on racism, climate change, or nuclear destruction. Perhaps we could unify on these existential threats? Yet even they are politicized, because what is good for humanity in the long-run may not be good for certain special interests in the short term. That’s the inherent dilemma in nearly everything — what is optimal for the common good, versus what is optimal for me. I thought maybe hostile extra-terrestrials might be another scenario, where humans from across the planet finally put their differences aside for the good of all. Although that’s science-fiction, the concept is not so crazy; former rivals can patch things up when they find a common cause. There don’t seem to be any hostile aliens on the horizon, however, which is probably a good thing.
Aside from climate change, nuclear catastrophe, or aliens, the BBC reminds us of another possible existential threat around which humanity can unite: a supervolcano.

Yellowstone. Source.
Yay?
The BBC article explains how the fallout from a massive explosion could do catastrophic damage not just in its immediate vicinity (Yellowstone, or Italy), but would create a “volcanic winter,” causing enormous environmental changes, covering a continent in ash, killing plants, poisoning animals, and would likely lead to an economic plunge and cause a very large number of human deaths. It would also create a economic crash and take a long time to recover. As Bill Bryson wrote in “A Short History of Nearly Everything.”
The ash fall from the last Yellowstone eruption covered all or parts of nineteen Western states (plus parts of Canada and Mexico) — nearly the whole of the United States west of the Mississippi. This, bear in mind, is the breadbasket of America, an area that produces roughly half the world’s cereals. And ash, it is worth remembering, is not like a big snowfall that will melt in the spring. If you wanted to grow crops again, you would have to find some place to put all that ash. It took thousands of workers eight months to clear 1.8 tonnes of debris from the 6.5 hectares of the World Trade Center site in New York. Imagine what it would take to clear Kansas.
The good news is that NASA thinks it might have a solution to prevent supervolcanos from erupting: by injecting water at high pressure very deep into the volcano to cool it off. Sounds great. Sadly, here too there is a dilemma — how much would it cost? Who would pay for it? Still, the costs of doing nothing would be a catastrophe, possibly extinction. I’m willing to bet that even here there are a few holdouts who are rooting for extinction. You won’t get one hundred percent agreement on anything, not even whether existence is worth it.
Yet for those of us who do want to exist, perhaps that might be enough of a reason to put the other disagreements aside? Can we agree on this? Just this one time? Stop the supervolcanos.
Um, you need to revise your answer to #2 above, since the question includes two alternatives. It either needs to be YES!-NO! or (better) reword the question.
Oh right. I see now.