How do you feel about crutches? I understand Kerry needed them in order to attend. ;^)
Some people cannot sit in the sun without a shade of some sort - due to eye sensitivity. It is not an affectation or comfort as would be the chewing gum that you mentioned, but a medical necessity.
You know that Laura Bush always looks very well dressed and groomed, so she must have needed to cover her eyes, because she surely is not wearing them to imitate Jacqueline Kennedy Onassis.
I repeat my answer...sunglasses are disrespectful.