Some mirrored compounds are dangerous by coincidence. It’s not that mirrored compounds are inherently dangerous.

Non-mirrored compounds can be incredibly dangerous, often because the organisms that produce them evolved to be dangerous. Take botulinum toxin, for example.

What would make mirrored life dangerous would be if it could escape to the wild and increase its biomass there. Non-living toxins can be deadly, but at least they don’t self-perpetuate. Even prions are limited in how they “reproduce.” They are nothing like the threat of viruses.

you’re missing the point so hard i’m not even sure where should i begin. thalidomide is synthetic, it didn’t exist before it was made for the first time in lab. there’s no way to tell which one is “right” and which one is “mirrored” this is nonsense. it is completely normal for pharmaceuticals to have different activities depending on enantiomer, sometimes one is weaker and one is stronger but both act at the same receptor/enzyme, sometimes one has one activity and one does something completely different, like slow down breakdown of the other, but most of the time one is active and the other does nothing.

the point of that thing is that maybe, perhaps, lifeforms based on d-aminoacids and l-sugars could evade immune response, and that’s rather speculative. not to mention incomprehensible barriers to making this all work in the first place. d-aminoacids exist in nature, if not all of them, and normal organisms can metabolise them. proteins made out of d-aminoacids degrade slower, but it doesn’t mean that there are no mechanisms to destroy these things. similarly i don’t think it’ll be impossible to generate immune response to wrong chirality bacteria, humans generate antibodies against things like PEG, important thing for antibodies is how external shape of these things looks like and this will be rather unique