[ASalazarMX]

This is such an interesting question, I hope it doesn't get buried before someone knowledgeable answers it.

We all know the more aggressive a pathogen is, the more it paints itself into a corner because it's burning its bridges. Something like airborne HIV would be really scary.

My guess is that airborne diseases are not weaker, but that evolution has selected for resistance against those because they spread fast among the population.

[lazide]

This is unfortunately just not correct in real life. It’s a good representation of general behavior/trends, but for instance Smallpox was around since at least 500 BC, and still had a 35% fatality rate until it was eradicated in the 70s.

The more times you roll the dice, the more often you’ll get that magic combo of lethal and highly transmissible. For the most part it doesn’t favor it, but that just makes it an outlier when it does, not impossible.