Almost all of my years of boating has been in Salt Water. I used fenders. No "Socks." My dockspace was in a protected marina. When I got back from sailing I still hosed off the hull AND the fenders with fresh water.
Salt water splashes on the hull will crystalize... and is very abrasive. I never had any indication that there was a problem with fenders abrading the gel coat. I am a meticulous SOB.
When I go to the lake with my little 20' runabout for two weeks...A rented cabin with dock space: The dock is broadside to the wind and wakes of the boats that go by. I bring my own 12 X 28 "Fend Aire" fenders. Totally oversize for the boat ..I hang them from the verticle posts on dock..but they work. I don't carry them on the boat. TOO Big. No Socks. No abrasion problems. Going on 15 years..same boat.
NB