I've heard a bunch of impractical proposals for ways to sequester carbon: pump CO2 gas into the ground, grow trees for the sole purpose of burying them underground where they won't decompose... and these proposals all seem impractical to me.
By contrast, it seems quite doable to allow people to consume single-use plastics, and dispose of them in well managed landfills. (I wouldn't exactly say we should encourage the practice, not until we have bioplastics in widespread use and green energy powering plastic production). Stringent efforts should be made to ensure the plastic is not burnt and is kept out of the marine environment.
Plastic is very chemically stable, it won't decompose and form methane or anything else, it won't bubble up to the surface, and mixed in with garbage it becomes unattractive for future generations to dig it up.
I'm also making the assumption that any oil not used for plastic production would be used instead in the transport industry or at least somewhere where it'll be put straight into the atmosphere. I think it's naive to think that if I forgo my plastic drinking straw, there'll be one more drop of oil remaining forever in the ground - it won't be left in the ground, instead it'll be made available to the transport industry.
I've tried to get an answer to this question from New Scientist, Australia's Dr Karl and basically every chemist or physicist I encounter and no-one can explain why I'm wrong. So it seems to me governments everywhere who are banning single-use plastics are doing the opposite of what they should be doing.