University of Adelaide's Roger Seymor has held the horizontal tack for a long time. A British documentary confirmed this. David Wilkinson in England says the neck of the Brachiosaurus, which was 30 feet long, was far too heavy to hold aloft.
The dinosaurs had long necks to conserve energy. The necks could be moved around in the search for food without moving the body. They were as long as was beneficial to save energy grazing. It was not really grazing like a cow, for example. Their neck were long tubes similar to a vacuum cleaner. They didn't do any chewing.