The Daishonin's Viewpoint on Admonishing Slander 

Most members of the SGI are people who take great pains to show respect to others and to be a harmonious influence in their homes and communities. Because of their compassionate nature, SGI members tend not to seek out conflict or take joy in criticizing others. Therefore, it is not easy or pleasant to confront others about their behavior, even if that behavior may be damaging to the individual, or worse, to many others. But if we truly care, we will confront that person. And if that person does not listen, we will responsibly warn those who may be endangered by that person's behavior. 

This is the attitude Nichiren Daishonin takes toward those who attempt to lead people away from the correct understanding and practice of Buddhism. His spirit in this regard can be seen in the following passages: 

"'If even a good priest sees someone slandering the Law and disregards him, failing to reproach him, to oust him or to punish him for his offense, then that priest is betraying Buddhism. But if he takes the slanderer severely to task, drives him off or punishes him, then he is my disciple and one who truly understands my teachings.' Never forget this admonition against ignoring another's slander of Buddhism. Both master and disciple will surely fall into the hell of incessant suffering if they see enemies of the Lotus Sutra and fail to reproach them. The Great Teacher Nan-yueh wrote, 'They will fall into hell with evil men.' To seek enlightenment without repudiating slander is as futile as trying to find water in the midst of fire or fire in the midst of water." 
"Admonitions Against Slander," The Major Writings of Nichiren Daishonin, vol. 1, p. 165 

"If you see the enemies of the Lotus Sutra and fail to reproach them, fail to bring their slander to the lord of the country, and remain quiet out of fear of others' reaction, you will fall into the hell of incessant suffering" 
Gosho Zenshu, p. 1077 

"If even a good monk sees someone destroying the teaching and disregards him, failing to reproach him, to oust him or to punish him for his offense, then you should realize that that monk is betraying the Buddha's teaching." 
"Rissho Ankoku Ron," MW-2 [2nd ed.], pp. 25-26

"Do not follow even the high priest if he goes against the Buddha's Law and propounds his own views." 
"The Twenty-Six Admonitions of Nikko," Gosho Zenshu, p. 1618

"No matter what great good deed one may perform, even if he reads and transcribes the entirety of the Lotus Sutra a thousand or ten thousand times or masters the meditation to perceive ichinen sanzen, should he but fail to denounce the enemies of the Lotus Sutra, he will be unable to attain the Way." 
"Encouragement to a Sick Person," MW-6, p. 24

"Though one may have been fortunate enough to be born as a human being and may perhaps have even renounced the world in order to seek the truth, if he fails to study Buddhism and to refute its slanderers but simply spends his time in idleness and chatter, then he is no better than an animal dressed in priestly robes." 
"The Fourteen Slanders," MW-3, p. 215

"The Buddha has constantly warned us, saying that, no matter how great an observer of the precepts a person may be, no matter how lofty in wisdom and well versed in the Lotus Sutra and the other scriptures, if that person sees an enemy of the Lotus Sutra but fails to attack and denounce him or report him to the ruler of the nation, instead keeping silent out of fear of others, then he will invariably fall into the great citadel of the hell of incessant suffering." 
"Letter to Akimoto," MW-7, p. 206

Source: Confirming Our Path of Faith: Temple Issue Handbook, SGI-USA Temple Issue Committee (Santa Monica, CA: SGI-USA {1999})