Leonardo DiCaprio at the premiere of The 11th Hour. Alex Berliner © Berliner Studio/BEImages When celebrities embrace environmental concerns, cranky naysayers pop up like toadstools after a rainstorm. But the mansions and private jets those critics seize upon, while easy targets, might not be the real problem. It might just be that green-leaning celebrities and their handlers need to open themselves up to harder questions from their media allies first, to help forestall that crankfest. At a recent press conference for The 11th Hour, Leonardo DiCaprio's eco-documentary, the ballroom of the Regent Beverly Wilshire wasn't packed with journalists eager to …