Forty years is a long time to wait, no matter how old you are, but the threat of war holds less menace for those not expecting to live to see it. The sacrifice the ship demands is more immediate, more personal to the older generations, even though they weren’t the ones to go. Self-sacrifice is justifiable, but sacrificing your kids or your friends’ kids is something much more wrenching methinks. All well and good to send people you don’t know, but because of the worldwide nature of the donation, there’s no way you wouldn’t; end up having someone you know go. One out of every ten people is a lot of friends and family.
And it’s not just personal attachments, the sudden departure of 10% of the population is not just 10% of the population under 35.
Statistics per the US Census folks we’ve currently got about 3,372,548,024 people in the right age group for donation, 1,189,024,391 of which are under 14 and probably not working for a living in the industrial nations (assuming child labor laws).
Now if we’re taking 660,000,000 people, that’s roughly 20% of this group, which is 20% of the current workforce and 20% of the workforce for the next nine years.
Since unemployment isn’t at 20% in most places, that means there won’t be enough people to fill the jobs. Which means lots of flailing and probably a surge in immigration to those countries which need workers. Which means and even bigger drain from those countries with higher unemployment rates, and I can’t see the governments of those countries being too happy with the sudden drop in followers/population.
Add to that the fact that Earth isn’t willing to just depend on Ship’s promises that defenses will be sufficient with what she’s given them. So there’s a gearing up of the war machines for the entire planet, and everyone is trying to figure out who’s in charge of what. All of the science and military types will have to work together in order to have anything useful to fight with in forty years (thirty-nine actually).
Plus you’ll have all the folks who take this as a religious Armageddon of sorts and that’ll bring the crazies out of the woodwork.
Which, erm, means life will be very very different for all the folks who remain on Earth, not just those that leave with Ship.