Most Americans are very suspicious of anyone asking you where you are going and why you are going just because someone with a little authority wants to exercise it.
If I am driving the speed limit and am pulled over by law enforcement, it had better be for a good reason and not a hunch.
We are seeing the same thing at airports now. If one opts out of the xray and chooses to be patted down, the TSA dude who is assigned to wait until a qualified officer to conduct the patdown shows up, will be asking you where you are going...all very innocently, until you realize he is fishing for information.
They do not need to know where I am traveling or why. As long as I am not carrying weapons, where I go, when I go there and what I intend to do when I arrive is my business and mine alone.
I do not like the idea of having to produce credentials to anyone on demand, absent probable cause.
Just because you are curious does not give you the moral or legal right to interfere with me and where I might be going.