Duty demands and requires, that what is right should not only be made known, but made prevalent; that what is evil should not only be detected, but defeated.

From Thoughts on the Cause of the Present Discontents (1770) by Edmund Burke.  

When bad men combine, the good must associate; else they will fall one by one, an unpitied sacrifice in a contemptible struggle.

It is not enough in a situation of trust in the commonwealth, that a man means well to his country; it is not enough that in his single person he never did an evil act, but always voted according to his conscience, and even harangued against every design which he apprehended to be prejudicial to the interests of his country. This innoxious and ineffectual character, that seems formed upon a plan of apology and disculpation, falls miserably short of the mark of publick duty. That duty demands and requires, that what is right should not only be made known, but made prevalent; that what is evil should not only be detected, but defeated.