Lying is a sin.
Thou art God, for good or for ill. If I am to respect that, then I must respect that your will is your own. The choices you make are your own. We make our choices based on our understanding of the Real. If I tell you lies, I am shaping your idea of the Real into something that is not Real. I am leading you to delusion, and I am subverting your will for my own purposes.
This is wrong.
Understanding is one of the Noble Trees, which bear the perfect fruit. To water the Tree of Understanding with water drawn from a toxic well is to pollute the Tree. To lie is to give in to the toxin of delusion — the delusion that my will is more important than yours, that my choices are more meaningful than yours. To lie is not only to drink of the poisoned well but to serve it to others.
If I must persuade you, let it be with the Light of Truth. Let the fruits of my Garden, tended with pure waters, go to seed in yours. We must never tell lies, for to do so pollutes two Gardens.
If it can be destroyed by the Light of Truth, it deserves to be destroyed.