What is morally wrong can never be advantageous, even when it enables you to make some gain that you believe to be to your advantage. The mere act of believing that some wrongful course of action constitutes an advantage is pernicious.
No man should so act as to make a gain out of the ignorance of another.
Ill gotten gains will be ill spent.
Strain every nerve to gain your point.
Nothing is so difficult to believe that oratory cannot make it acceptable, nothing so rough and uncultured as not to gain brilliance and refinement from eloquence.