In Act 1 Scene 14, while investigating about the murder of Mr. Douglas, Sherlock Holmes had to be blunt with Barker

Another clue discovered soon after is a bicycle, concealed just outside the house grounds. Interrogation of the house servants reveals little, and after Mrs. Douglas, wife of the murdered man, and Cecil Barker, a friend of the family, are questioned, Holmes reveals to Watson that he believes the two are in a conspiracy together. I think your last question is really a question of opnion. Some might think a greater cause gives people the right to exploit others.