If you good reasons (for example healthy reasons) to rationalize your motive(s) foir killing insects, for example ( by the way: it was your example) , then this rationalization is not deceptive.
Health is always a good reason. It is good resp. okay and especially healthy to be self-preservative. No living being is capable of living without self-preservation. Life is self-preservation.
So I ask you: Why should it be better for you to be killed by other living beings (for example: insects)?
That’s right. And if you asked that insect and were capable of understanding its answer, then you would soon know that the insect would make the same statement as I do.
In an effort to be rational, I suspect that you should stick to this definition for “rationalization” in English:
The educated and rational man knows that it is the negative connotation of every nuance that is given higher priority regardless of the intent of the speaker.
Hence, all rationilzation is deceptive even if we take life is self preservation as the so called “meaning of life” (which is a rationilzation in itself).
There is still a difference between a rationalization and an explanation. Self-preservation is possibly the only explanation that isn’t a rationalization.
Self-preservation is merely incidental, not primarily or meaningfully significant. You simply need to happen to keep existing if you’re going to have meaningful experiences, but “existing” and “survival instinct” (which actually doesn’t even exist) are just unrelated conditions that are necessary for actually significant things.
Life didn’t evolve and develop because it needed or wanted to survive. Life doesn’t even “want” to survive, it simply tends to act in certain ways that over time and a large enough sample size don’t end up leading it into non-existence. This is a consequence of embedded instinctual frameworks that causally determine what life does and why, in the presence of certain stimuli.
As Parodites said, when you eat your jaw muscles are simply engaged in a kind of non-conscious spasm that has simply been refined over millions of years of natural selection to do a decent job of actually tearing up whatever you put in your mouth. It’s not teleological.
Or as Nietzsche said, we don’t eat because we are hungry, we are hungry because we eat.