I have only seen one (1) lens scratched in my long career. Fingerprints that destroyed a special coating, yes, but keeping a lens clean is a better lesson than sticking a filter on the front for "protection". Get a lens hood for progtection.
The problem with the constant use of a filter in front of a lens is you are sacrificing the sharpness of a lens that has ben engineered and balanced with multiple elements out of different types of glass that also minimizes the number of glass to air transfers of the light as it enters the camera. In other words, you are losing an edge in sharpness by leaving a lens on the camera all the time.