Charlie Jane Anders says that if we meet intelligent Space Aliens, we’d probably try to eat them (and we shouldn’t). I agree, because people are horrible, but I also think we shouldn’t because at the least we’re going to get Space Diarrhea, but we’re probably just going to get Space Death.
Anyway, I made a video. Unfortunately, I didn’t script it, but just charged off extemporaneously, which means it ended up about an hour long. Sorry. College professor. Wind me up, I talk for an hour about anything.
The summary: earth life maintains mutual compatibility (more or less) because of its common origin, 4 billion years of co-evolution, and because specialization and cooperation maximizes efficient extraction of resources. Aliens have none of that, and are quite likely to have diverged biochemically in ways that are inherently inimical to our biochemistry, and we have not had any opportunity to adapt to their differences. I also suggest that one hypothesis to explain the so-called Fermi Paradox is that habitable worlds evolve such different detailed chemistries that they are basically tainted toxic soups to other species, and that any sensible starfaring species would flag stellar systems with living biospheres with a great big biohazard symbol. Mars-like worlds which lack any native life (presumably) but are terraformable might be the optimal target for human colonization.