Well, taken as a statement on it's own, I think I disagree. I think that maintaining your honesty with yourself is pretty important. When you start lying, where do you draw the line. I think that when you validate, you are giving your partner the emotional side of agreement, without necessarily ageeing with the facts.
Him: The sky is green today. You: It does look like it might be green, doesn't it? or You: I can see why you would see it that way.