"We are writing to express our shock and dismay at the addition to the Guardian's US commentary team of a man who has openly called for the killing of people on humanitarian missions to Palestine, people who have included the Pulitzer-prize-winning author Alice Walker. The extreme views of your new freelance contributor Joshua Treviño, whose columns will appear on your Guardian US website from tomorrow, are no secret. In 2011, he used Twitter to urge the Israeli army to murder unarmed US citizens who were preparing to sail from Greece on a flotilla to Gaza. Treviño tweeted: "Dear IDF: If you end up shooting any Americans on the new Gaza flotilla – well, most Americans are cool with that. Including me." He also backed a tweet which called for the sinking of the flotilla, which would have endangered the lives of all on board, and likened this peaceful mission to a "Nazi convoy"."