Authentic from the Defective

"When some people said to Imaam Ahmad Ibn Hanbal (rahimahUllaah) that they felt uneasy about criticizing people, he replied, 

'If you remain silent and I remain silent, then who will make the ignorant person aware of the authentic from the defective?'" 

[Majmoo'-ul-Fataawaa of Ibn Taimiyyah (28/231)]