I guess I've never really thought about it from an unbiased perspective before. How bad are landfills if they are done in some sort of long-term strategy? You can cover over the landfill and make new land with it (many parks are basically this). But I worry about things like battery acid and other chemicals seeping into the water table or causing who knows what damage to the soil.
At least on its face if you're putting the plastic deep in the ground, from whence it came, maybe that's a decent intermediary solution.
But I would also agree with anyone who says its not sustainable. The amount of waste we produce seems a little insane compared to other creatures on the planet.
The Earth has 5-10 billion years left at most, whatever we do to it (unless we reach the point of being able to change its orbit). Less if we're unlucky and get hit by an asteroid etc.. So there's no such thing as truly sustainable, only "good enough".
Im not sure if you correctly understand what the word "sustainable" means. X is sustainable IFF you can keep doing X forever and not have it kill you eventually. "Seems to work" is perhaps a sub-optimal policy objective.
Pretty much every physical object we had started out underground and was mined by human or plant activity, except for the minerals that are synthesised directly from the air.
It isn't a hill I'm going to fight on, but 'land is a finite resource' has, to me, always meant arable farmland and prime coastal real estate. There is no actual shortage of land. At best, there might be a shortage of prime away-from-water-table-with-less-permeable-rock-surroundings sites that are ideal for landfill - but I doubt that is true.
For example, the deepest mine is about 4km deep, and about half the atmosphere is within 5km of the surface of the earth. Running out of landfill space in that sense is like running out of oxygen. The only limits are transport costs and making sure the landfill is either non-toxic or kept well away from water (which, economically speaking, might be a substantial limit but plastics are clearly quite inert, because we store food in them and they apparently don't degrade).
EDIT But the key point here is that these costs aren't externalities. The people paying for them are the consumers who are buying the plastic. If landfill costs go up, municipalities will start to charge more for waste disposal and consumers will favour products with less packaging.
