To play devil's advocate, there are not enough raw materials on earth to produce close to the amount of necessary devices that would fill the ipv6 space.
I can be convinced that this large amount has other benefits, but not that this number of IPs was needed for futureproofing.
Well, there's a couple other considerations. For one thing, some devices may have multiple IPv6 addresses - perhaps even entire slices of it. For another, having additional bits to work with allows people more room to divide their subnets into future-proof chunks without risking ever running out of IPv6 space - something IPv4 could never really afford in the first place. What would be considered large chunks of IPv4 are a drop in the bucket in IPv6.
I think the main idea is that you want to have plenty of space both for growing horizontally and vertically, at least enough to where you can't even imagine exhausting it in either direction. Giving massive private and public address space without need for NATs effectively provides this.
Also, hey, who knows. There isn't enough raw materials on Earth, perhaps, but maybe there are enough raw materials in the universe. Who knows for sure if the Internet always be confined to just Earth.
Unless you get faster than light communication, the interplanetary protocols will require advanced collision handling which TCP does not provide anyway, and all kinds of "on-line" access will be impossible due to light lag.
It is needed for future proofing because the idea is not that every single IPv6 address is used.
To simplify routing, only a small fraction of the address space will be used.
At least that's how I understand it. Think of it like this - GPS coordinates are longer than post codes and less efficient for storing the location of people. But as a bonus finding someone's location using coordinates doesn't require a huge database of post codes.
Similarly, coordinates have a huge address space - every location on the planet, but we don't expect people to actually live at every location - in the ocean etc.
