If we take plant, turn them to plastic that doesn't regards quickly, then bury them, we're sequestering that co2
Oil for plastics is more akin to the use of any other natural resource in a product or good.
The above commenter indicated 'issues with extraction', well yes, but we have the same issues with extracting everything else. Also, frankly, most oil extraction is not very damaging directly - if we were only using oil for plastics, we'd probably only use the easiest to access oil, like from the Middle East where we pop a straw in the ground and that's it aside from refining.
Burned 'anything' that we put in landfills is actually better than raw garbage as it's considerably reduced and more dense - but it's still landfill.
We should strive for a solution that doesn't require landfill.
Oil is not evil. It's the Co2 bit that's a problem.
The problem you missed was at least to some extent recycling: we can't reuse the material at all, and while theoretically burning is practical, we still don't separate everything and burning still leaves a byproduct that has to be buried.
I suggest the alternative is going to have to be something that truly disintegrates, i.e. more organic.