As Cove said, windows make sense for the simple fact of seeing what's going on outside. If you entirely relied on the viewscreen, you are blind or reliant on sensors when it is inoperative.
Wouldn't that really depend on how good your eyesight was? An anomaly might be invisible to the naked eye, or a hostile thousands of kilometers away as it opens fire (or even behind the ship).
I don't have a problem with it as a window that has displays and graphics on it, but its main function should be as viewscreen, which shows all to the Bridge staff.
Commander Austin Harris, First Officer, Deep Space Nine (by FltCpt. Bossco)
8.01 - Darkest Before Dawn
(Chapter 8 added, 12/09/2015)