noun

a person who disparages someone or something.

the island, say its detractors, has been devoured by development

critic,disparager,denigrator,deprecator,belittler,attacker,censurer,fault-finder,carper,backbiter,caviller,reviler,vilifier,slanderer,libeller,calumniator,defamer,traducer,mud-slinger,knocker,nitpicker,asperser