The KJV uses the same root, simple, for the “naive” (6612a) and “simplicity” (6612b) of the NASB. The difference in the Hebrew is that one is a noun and the other an adjective. The Hebrew word for “simplicity” (6612b) must have a different meaning than the one the Richard Foster uses when he praises it in his book on simplicity.
The concern is about people who always accept things at the surface level. The simple person never looks beyond the superficial presentation. We have had presidents who were this way. They lacked discernment into human character. It is not just for the lowly. This is what Jesus was trying to get across.
(Matthew 10:16 KJV) Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves.A bit of cynicism can be healthy when it comes to questioning what goes on in our world. In reality it is being realistic even when people call you negative.
So? All is not sweetness and light. Sin is rampant. We need to be alert, mature and discerning. If we, God’s servants, are not alert, who will be?