More than a hundred people gathered on the steps in front of the Georgetown Law Center here on Tuesday in anticipation of an appearance by Attorney General Jeff Sessions. Inside, Mr. Sessions would be discussing one of today’s most pressing topics on college campuses: free speech. But outside, a group that included students and members of the law school faculty pointed to the irony that they had been denied access to the hall where the attorney general would speak — placing him in precisely the kind of safe space that he was there to criticize.