Actually, a lot of the more whacky environmentalists HATE man-made reefs. I'm a saltwater fisherman (DE, MD mostly) and the envirowhackos fought tooth-and-nail against a plan to dump hundreds of old NYC subway cars to form artificial reefs off NJ...and they won (Delaware ended up taking them.) Touted a bunch of crap about the "asbestos" in the cars (like asbestos underwater does anything to anybody, or anything.)
They whine about the oil that continues to seep from the USS Arizona, too.