Asking for and ID for no other reason then the fact the person is open carrying in a place where it is legal, in and of it self is infringing on that persons rights. I would have to say ANY time a persons rights are infringed on in any way (even if slightly) is a good time to get defensive.
I feel stopping me to see my ID because i am carrying a gun to "be sure im not a felon" is about as offensive and out of line as it would be to stop me for ID as I carry my child to be sure im not sex offender.