Edited

I think you've made very excellent points, but as I see it, it's all more complicated. Some of the basics you've summarized are very true, but you've got to think about the heavy metals that would make your efforts so complicated that even "boric acid will not help you to get rid of roaches in case they are coated in i.e. lead" - to use your good "roach killing" example/methodology.

So you've got a good tool (boric acid) that works perhaps 70% of the time for the "non-metal impacted" roaches - but no matter how much boric acid you use and for how long, your "metal-coated" roaches will not touch it and ride happily all around it, or maybe better yet, will use this boric acid as their weapon against your efforts.
Then what?
You've got to find out how to "destroy" their
"coat". The worst yet - they might be coated with a "bioweapon" coat that is basically non-penetrable. Because it was made to be like that and nothing would break it. What then?
So after you do your research and equip yourself with a knowledge "how to", then you've got to deal with that "coat" first, before you can apply your normally workable tool (boric acid).
And then it is when it's start getting pretty complicated, because almost all pathogen organism are extremely intelligent and know how to "fool" you and your immune system and your body - they always keep changing their coat a little bit (biofilm constant changes), plus they bind with their "friends" inside you (other parasites) forming layers that seem to be extremely dificult to penetrate.
Then there are species out there (or in there better to say) that simply do not react to anything you do - maybe they become treatment resistant, maybe you just simply did not discover (yet hopefully) what "touches" them to destroy them.
If you're working on all this from the "researcher" position - meaning you learn as you go on, then it is always try and miss or try and hit. But how many of us are trained biologists (or someone who studied the animal/ parasite world) and knows possibly their "weaknesses" - meaning if you know everything about their life, possibly you can use that to your advantage and outsmart them, knowing everything about them so well that you know how to "get them".
Definitely I agree with you a 100% that there's nothing you can do to prevent them (they truly are anywhere at any given moment)- impossible and waste of efforts, agreed. Tweet