Single-use plastic waste is good. It sequesters carbon. https://www.scientificamerican.com/article/wait-plastic-can-...
Keep in mind that still significant portions of (fossil based) plastic waste are incinerated as well. And scale matters: in the country where I live roughly 30kg of plastic waste is per person per year. That's in the order of magnitude of a single tank of gas of a small vehicle. In other words: the sustainability problem with current-day plastics is not so much in it's carbon footprint, but more the damaging effect to various ecosystems and human health.