In the USA, landfill space concerns are based on a hoax. Landfill space is a function of landfill development, and there’s no shortage of spaces to create landfills.
I am not talking about running out of space in general. I am talking about taking a hill covered with trees or farms, and turning it into a hill of garbage. Surely you can see why I would prefer a natural hill?
If you can burn it, there is no point in burring it. We're still taking a lot of stuff from underground and burn it for energy, why not burn the stuff we already have above ground?
Landfills amortize the carbon emissions. Keeping the plastic's carbon temporarily sequestered in a landfill puts it somewhere other than the atmosphere. Eventually we'll have to do something with all that carbon, but we're better off burying it until we get a better handle on emissions in general.
You would be right, IF we were to not take out any other fossil fuel to burn. But to bury the plastic now it just means we will dig for an equivalent quantity of coal, oil or gas to burn. We will burn some stuff regardless, we might as well burn what we already have, instead of burying it and digging for new stuff.