The home crowd in Turkey will be cheering against the USA team in every game they'll play. They will be in hostile territory from beginning to the end of the tournament. Majority of the people will definitely want to see Team USA go down in defeat. Team USA will be the team to beat in the WC in Turkey.
There's no question the USA will be playing before hostile crowds during their tournament run, both from the Turkish fans and from fans of other nations. I imagine most of the hostility will emanate from people who want to see the favorite lose; in this case the USA, Spain or whoever else.
But some of the whistlers and boo-birds will be expressing long standing, often politicized anti-American sentiment, and it doesn't help that the NBA players are highly paid, perceived-to-be-spoiled/arrogant athletes that deserve some measure of come-uppance in their opinion. I get the sense that, unlike Brazilian soccer players, who, like their American counterparts are famous, highly paid and supremely skilled at what they do, US NBA players don't get the same reverence, at least not to the degree that past "Dream Teams" got. When Brazil's soccer team plays abroad, with the exception of places like Argentina or Uruguay (traditional rivals), opposing fans of Brazil (or just neutral fans in general) cheer their home team to victory rather than behave openly hostile towards Brazil because they're "Brazil." Not so with the US. There's definitely more of a bloodlust to see the US lose because of the issues I stated above.
Unfortunately, despite how successful our national team has been internationally, Americans have among the weakest fan support for national teams travelling abroad. In fact, the average American probably isn't aware this tournament will be going on. The best the US players can hope for as far as support will be from US military personal stationed in Europe, and even then their USA! USA! chants will be drowned out by boos and whistles.
I agree with D-town. In the long run, all the booing and jeering won't have any effect on the outcome in most games. The US won't have any trouble with teams they're suppose to beat, but against Spain, the hostility might make a difference. NBA players are use to playing in hostile environments, so I'm hoping that gives them an advantage once the tournament reaches the critical rounds.