We're wired to come up with simple heuristics like "smaller than 5 microns bad" and "larger than 5 microns fine". It's much harder to hold a true model of the world in our heads: a list of every different disease, how big particles containing it need to be to lead to respiratory infection, and how each type of virus and bacteria behave under different atmospheric conditions (humidity, temperature, pressure). While we can try and not rely on over-simplified heuristics, to really ensure that our heuristics aren't killing people we'll need to eventually offload a lot of this type of fine-grained simulation/prediction to software.