Sam, it looks like the bird reference was borrowed to show how things aren’t black and white.
The thing with not being seen is not optimal. It works when you say that something that you can’t see is not Assur and was not included in the Issur of the Torah. It is quite another thing to say that if you can’t see a phenomenon then it doesn’t happen, to the extent that the one it pertains to is considered to be in another class.
The funny thing with the Pachad Yitzchok is that if Rav Yosef is wrong then we should be Meikel, not Machmir. We Pasken like the Chachamim so if there is no difference between the Kinah and other bugs we can kill them all. YIPPEEE!!