That is not true.
The words "rational“ and "rationalization“ have the same root. What you are saying is that, for example, all enlightenment is "deceptive“. And that is - of course - not true.
Political correctness, psychologism and sociologism, for example, are deceptive.
So you do not kill insects?
Do you live according Ecamndu’s "rule“? 
I have no idea what you mean by enlightenment.
I do not have an emotional need to kill insects and if I did then I would have to rationalize my emotional needs.
You really do not know what “enlightenment” means?
I didn’t say… I don’t know what enlightenment means.
And there could be good reasons (for example healthy reasons) too to rationalize your motive(s).
Okay.
Again: That is not true.
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.
You forgot to mention why good health was a good reason.
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)?
You are making the statement that your health/life is more important than the health/life of an insect without any good reason.
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.
How is any rationilzation of killing each other based on this knowledge not deceptive?
Like I said: Life is self-preservation.
So I ask you again: Why should it be better for you to be killed by other living beings?
If you did not preserve your life, you would just die.
Yes, I will die despite all of my efforts to preserve my life and no amount of killing other people or other animals will preserve my life.
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).