No offense, but there’s a lot of assumptions there. Who says that alien species would even have DNA or chirality or amino acids at all? When considering what we might meet outside the confines of our solar system, one might consider it wiser to think outside the Terran box, as it were.
I would further point out that even if they have kind of structure you expect, one that would supposedly rule out any chance of biological compatibility, one thing that we should assume as a universal trait is evolution i.e. just because they’re not wildly compatible now doesn’t mean they won’t be in one Terran year (as the influenza viruses keep reminding us).
Sterile worlds in the Goldilocks zone might require a heavy lift when it comes to terraforming, but they’re our best bet.