Understood and respect your decision.
However, most online vendors nowadays will code their promotion codes for one-time-use only if that's their intention -- thus, it simply won't work if there's an attempt to use it a second time.
Others openly encourage (or at least don't explicitly discourage) coupon code sharing as a form of viral marketing.
Again, not disputing your decision not to share. As an online marketing professional, I just wanted to give a different perspective.