Historically burning trash has been a net win because food scraps decompose to methane if landfilled and if used to generate electricity and/or local heat networks the trash displaced fossil fuels from the grid.

If your nation is diverting enough organic waste from household waste, and has enough low carbon generation in the grid mix then the calculus changes and you can start worrying about the fossil plastic in the mix, but the biggest impact there is to intercept the plastic early and recycle it.