We do not have an alternative to petrol based plastic for our current economy. Yes, we can make plastic from non-fossil biomass, but it's energetically feasible to replace petrol based plastics. We don't have the landmass, fertilizer, ... to switch completely. (Especially, if you consider the big picture: Biofuel, carbon sinks, food security, ...)
In a way petrol chemistry bought the planet some time before being destroyed by us. It saved the whales and prevented ecological exploitation in the colonies.
Since plastics are used amass not just for stupid junk, but also critical for e.g. medical single use items, sanitation and so on, we shouldn't just think about pollution. Although the thought of eating up to 7g of plastics a day doesn't sit right with me. (Little known side fact: It's not just obvious "plastics", silicone and paint does contribute to microplastic accumulation too.)
Our survival very much also depends on preserving oil reserves for essential use cases of petrol chemistry. Carbon neutral alternatives for many things usually come with an increase in another factor (energy, land use, non renewable resources) which makes them in concert unable to replace fossil energy/chemistry.
Resist.
REDUCE.
Reuse.
Recycle.
Rebury.
> ... but it's energetically infeasible to replace petrol based plastics
(2nd paragraph)
I am using this throw-awayish account with a lacking mobile app and cannot edit. So by all means, everyone, consider selimthegrim's comment a shame-edit to mine.
No, it isn't. Plastic is only showing up in large quantities in areas where it shouldn't, and occasionally hurting some animals. Microplastics in particular may become a problem at some point, but then again, maybe they won't. We aren't sure. And either way, it's not causing problems just yet.
Greenhouse emissions are what's killing the planet. Manufacturing plastics is a part of that, but so is power generation, and thus all "purely digital" activity.
It's a point that people often confuse. Microplastics are bad, and emissions are bad, but they're bad for completely different reasons. Climate is what's an existential threat to civilization, and what we need to focus on right now. We can deal with microplastics later, if we survive that long.