For all the risk facing Facebook when public hearings start on Tuesday, top aides on Capitol Hill worry that lawmakers could drive themselves into serious peril if they take detours into fringe theories or shaky political grievances. Yet that is precisely what many expect their bosses to do when the cameras go live. Facebook founder Mark Zuckerberg made the rounds on Monday for private meetings with lawmakers ahead of Tuesday testimony before the a joint session of the Judiciary and Commerce committees, to be followed up by a turn in the House on Wednesday.