You make a good point Tor, all people, usually in late childhood come to realize that invisible germs are out to get you and perhaps JWs are institutionally snagged at this moment of development.
It is at an age when dependency on parents and authority figures remain in place and to the susceptible mind, learning about germs can be linked to an exaggerated sense of contamination.This notion of contamination has many religious manifestations (look at the absurdities of the Mosaic law). JWs are constantly exhorted by their task masters to stick together because of this same drive of fearful contamination of "the world".
No doubt to the JW mindset the idea of global "cleansing" of non believers seems the right answer to the contamination issue......forget that they are talking about the precious lives of 7.5 billion sentient, loving humans, who are reduced by JW thinking to mere dirty scum.