Casino opponents have sharply criticized the state gambling commission’s choice of a prominent casino lobbyist to be the keynote speaker at the commission’s first public educational forum on the industry, planned for next week. The panel’s choice of Frank Fahrenkopf, president and CEO of the American Gaming Association, was a mistake, said the non-profit organization, Stop Predatory Gambling, which is based in Washington DC. The letter was co-signed by an outspoken opponent of casino plans at Suffolk Downs.