[yyyk]

>Reverse chirality autotrophs sound like a scary sci-fi novel plot

I doubt this. 'Not being digestible' is very far from 'being invulnerable' or even 'being able to spread quickly'. The kingdom of life has many ways to kill stuff, ways which don't care about chirality, and our typical R-sided lifeforms have all the evolutionary 'motivation' to come up with new ways just the off the competition. That's before humans get into the picture, which we have the tech to do.

There may be an accumulation of non-digestible stuff until nature reaches a balance. However, there's a very large recent accumulation of non-digestible materials called 'plastics', and while somewhat harmful, they're not a life-ending threat. Nature is already finding ways to process these materials[0].

[0] https://en.wikipedia.org/wiki/Plastic_degradation_by_marine_...

[echelon]

Sure, but I did say "sci-fi". And I think there are a lot of unaddressed points.

Plastics don't self-manufacture. You might not be able to control the rate.

Just because you kill something doesn't mean you break down its carbohydrates. Reverse chiral organism skeletons could bioaccumulate and we could have a situation similar to the Carboniferous.

Someone might be able to synthesize a bacteria in the lab given enough time and effort from an organism that proliferates quickly. It doesn't have to capture all the carbon. Just out-compete a keystone species. Plankton, mycorrhizae, etc. Or attack a large percentage of the plant biomass.

[yyyk]

>Plastics don't self-manufacture. You might not be able to control the rate.

The rate is limited by the process. Since no precursors exist, it must 'self-manufacture' from scratch. This has inherent limits even before introducing competition for food, poison, predators that eat you even despite them not being able to really digest, etc.

>Just because you kill something doesn't mean you break down its carbohydrates. Reverse chiral organism skeletons could bioaccumulate and we could have a situation similar to the Carboniferous.

So you don't break it down. Nature will have plenty of time to adapt. Humans will step in if needed.

>Someone might be able to synthesize a bacteria in the lab given enough time and effort from an organism that proliferates quickly.

That's an incredibly messy way - create an entire L-chiral biochemistery - to get a weapon which doesn't have a setting between 'kill everything' and 'do rather little' (IMHO, the second being much likelier). There are far worse and more directed things one can do with a lab. Even the absurd 'kill everything' goal is far more likely to be reached in different ways.