That's the problem. Mirror life may not be a problem for the biosphere in the long run but it could totally be a problem for humans in the short run.
Mirror life can only use the fats and a few amino acids of the normal life. All sugars have chirality so they would need some enzymes to east their own mirrored sugars and another set of enzymes to eat normal sugars. Also, most amino acids have chirality and they would have to reverse them or make their own.
So even if someone waste a few gazillions dollars to make mirror life, it would not be able to eat most normal food.
Until mirrored life evolves enzymes to eat non-mirrored sugars, mirrored life will be at a large disadvantage.
But with exposure to our environment, replete with non-mirrored sugars, that sets up a large evolutionary pressure in the direction of finding those enzymes, in addition to the mirrored enzymes they will already have for eating mirrored sugars.
With such evolutionary pressure, it seems plausible mirrored life will evolve those enzymes, even though non-mirrored life appears not to have done so, or at least not retained it. Because there has been no equivalent evolutionary pressure for non-mirrored life to eat mirrored sugars.
If mirrored life does evolve those enzymes, due to that asymmetric evolutionary pressure, then instead of being at a disadvantage, it might give them a temporary advantage over non-mirrored life.
Also cellulose and starch are very similar, they are chains of glucose, but bounded slightly different. We can split only starch, but we don't have enzymes to split cellulose, were "we" includes cows and a lot of animals that would really love to digest cellulose.
I think some bacteria can digest weird sugars, even the mirrored versions, but they are more efficient digesting usual sugars.
Until mirrored life evolves enzymes to eat non-mirrored sugars, mirrored life will be at a large disadvantage.
But with exposure to our environment, replete with non-mirrored sugars, that sets up strong evolutionary pressure in the direction of finding those enzymes, in addition to the mirrored enzymes they will already have for eating mirrored sugars.
With such evolutionary pressure, it seems plausible mirrored life will evolve those enzymes, even though non-mirrored life appears not to have done so, or at least not retained it. Because there is no equivalent evolutionary pressure for non-mirrored life to eat mirrored sugars.
If mirrored life does evolve those enzymes, due to that asymmetric evolutionary pressure, then instead of being at a disadvantage, the ability to eat both types of sugars might give them a temporary advantage.
