Allah (SwT) is the ultimate judge of values, we may not propagate evil save with notable exceptions such as open correction of injustice by men in authority, as is laid down in the Holy Verse:
''Allah loveth not the evil should be noised abroad in public speech, except where injustice hath been done; for Allah is He hearth and knoweth all things'' (Al-Nisa: 148)
There are ways and means of propagation of evil, such as sensation-mongering, it may lead to more evil by imitation, the sensation-mongering could be by means of communication such as TV, cinema, by a work of art—novel, drama. It may be malicious gossip or it may be by malevolent slander/libel. Such a propagation of evil is absolutely forbidden. However, if it takes the shape of a public rebuke or correction or remonstrance, without malice by a person in authority, in which case the exception applies. It implies wrong or injustice must be corrected openly to prevent its recurrence. Exception may also apply in case a person otherwise not vested with authority, acting from motive of public spirit to help someone who has been wronged. Or, in case a person has suffered a wrong and seeks public redress.
Further, it is ordained:
''Whether ye publish a good deed or conceal it or cover evil with pardon, verily Allah doth blot out (sins) and hath power (in the judgement of values) (Al Nisa: 149)
Allah (SwT) is the ultimate 'Judge of Values' as He has the ultimate 'Power of Judgement' (Qadir in Quranic idiom). Allah (SwT) forgives what is wrong and is able to fully appreciate and judge the good deeds, whether we publish them or conceal them.