Sure, we should certainly be active about shaping the course of progress.

In the Hornblower series of novels, at one point Captain Hornblower surrenders to the enemy during a naval battle. He is captured by the French, but later escapes. When he gets home, he's put on trial for surrendering. They finally acquit him when it is revealed that he had lost something like half (maybe two-thirds?) of his crew—basically massive casualties. But surrendering was considered guilty until proven innocent.

This pairs well with Scott Alexander's Kolmogorov Complicity And The Parable Of Lightning

Yes, they would not be made from mirror components!

Synthetic cells aren't inherently dangerous if they're not mirror cells (and aren't dangerous pathogens of course).

Failure to detect other life in the universe is only really evidence against advanced intelligent civilizations, I think. The universe could easily be absolutely teeming with bacterial life.

Re “take steps to stop it”, I was replying to @Purplehermann

The asymmetric advantage of bacteria is that they can invade your body but not vice versa.

I think until recently, most scientists assumed that mirror bacteria would (a) not be able to replicate well in an environment without many matching-chirality nutrients, and/or (b) would be caught by the immune system. It's only recently that a group of scientists got more concerned and did a more in-depth investigation of the question.

Yes, antibodies could adapt to mirror pathogens. The concern is that the system which generates antibodies wouldn't be strongly triggered. The Science article says: “For example, experiments show that mirror proteins resist cleavage into peptides for antigen presentation and do not reliably trigger important adaptive immune responses such as the production of antibodies (11, 12).”

Given that mirror life hasn't arisen independently on Earth in ~4B years, I don't think we need to take any steps to stop it from doing so in the future. Either abiogenesis is extremely rare, or when new life does arise naturally, it is so weak that it is outcompeted by more evolved life.

I agree that this is a risk from any extraterrestrial life we might encounter.