In the future, John might change his mind about keeping it quiet, but right now this whole thing is brand new to him. He has, admittedly, had a few secret fantasies about doing just this to Sherlock. But that was the thing, they were secret.
Moving up, John kissed Sherlock again, this time, his hand trailing down the detectives stomach, and to the button on his jeans. He then released Sherlock's wrists.