Ironically, plastic -> oil is worse for the climate than just leaving the plastic in the ground. Plastic, which famously doesn't degrade (though that's not exactly true; there are bacteria which are evolving to eat the stuff) is just another name for long term carbon storage. Obviously we'd much rather have that in a properly designed and build landfill than in the ocean. But turning it into oil and burning it is just putting more CO2 from oil into the atmosphere.