as for the ¨we have to lie in some cases¨ I strongly disagree with that.
There is never a good reason to lie
Many, many cases in history disagree with that. Pretty much any case where we've had ethnic cleansing going on and people protecting them, have been incredibly good reasons to lie, and that's... just the start of a very long list. Deception and dishonesty are fundamental parts of human interaction, and often for the better. As I've noted elsewhere, most of us wear clothes, and affect behaviors intended to deceive -- to present a message to others that reflects a picture of ourselves that is not a true one. We smile when we are sad, we walk with confidence when insecure, we give pleasantries to others even when the doing so is falsity. All... very normal, and often done with the intent of bettering those around us -- making their day brighter, even when, strictly speaking, your "Good day" or whathaveyou is a lie. We hide many truths of ourselves, and deceive, misdirect, and so on.
The lies we tell children in schools -- about math, about history, about science -- are manifold, and often done for genuinely good reason; some things really can't be understood by most at points in their development, and simplification is an appropriate path in that case. Tell a small lie, now, so that the larger truth is able to be learned, later. Even in churches, from what I've seen of sunday schools and whatnot, the practice is quite strong.
It's hard for me to see any conclusion otherwise. We have many reasons to lie. Many of them good. Almost every aspect of human civilization has screamed that from the rooftops in the same moment they condemn dishonesty on the streets. In the face of starvation, pain, death, and all sorts of other horrors this hostile existence forces upon us, the lies that bind together societies are not sins, but virtues.
... which isn't to say that all lying is good, of course. But the control of truth, including its fabrication, is a tool. It is not, itself, something with necessary moral character. There are good lies, and bad lies, just as there are truths spoken with good intention and truths spoken foul.