I don't disagree with anything on this chain but I think things like hypothetical miles deep landfill can't be worse than burning, it'll stay there for million years and the next iteration of life to do the same discussion as being done here.
To me a "miles deep" landfill sounds like a wonderful way to contaminate groundwater.
I think it's facile to imagine that the Earth is large, thus that burying something can "make it go away".
But the Earth is also an incredibly dynamic place over long enough time scales (which for the purposes of this discussion can simply mean decades or centuries) so much of the lightweight matter you bury deep in dense rock can find a way to buoy back top the surface far sooner than in millions of years.
We know for sure that CO2 is a huge problem in the next century, and even earlier. We are already seeing massive impact from global warming today.
Any theoretical other concern from possible impacts of plastic in a landfill (which already will contain many other unknown pollutants) is at best secondary, unless we have some solid evidence otherwise.
Consider also that some significant amount of plastic in landfills is inevitable regardless of any sepatate collection policies. Especially with current recycling practices, you are encouraged to only separately collect certain kinds of fairly clean plastics. If you have a dirty styrofoam container that you just ate out of, you're not even supposed to throw that in the plastic recycling - so it will go to a landfill anyway. This means that landfills have to be mindful of potential plastic pollution even if we burn a lot of the plastic we use.
Plus, if we're truly worried about the health impact of plastic use, the only solution is to massively reduce plastic use. The fact that we "cleanly burn it" instead of letting it seap into groundwater is not going to help one iota when we store and transport and sometimes cook much of our food directly in it.
