Some people might wonder what is good about accusing those followers of the Pure Land and Zen Buddhism, making enemies of them. In response, I will cite the Nirvana Sūtra: “Suppose there is a virtuous monk who does not accuse anyone of harming Buddhism, does not try to purge or punish him. You should know that such a monk is an enemy of Buddhism. In case the monk accuses such a man, purges, and punishes him, such a monk is a disciple of the Buddha who truly follows Him.”

Grand Master Chang-an explains this in his Annotations on the
Nirvana Sūtra:

“Those who destroy Buddhism are those within Buddhism working against Buddhism. Those heartless people who keep friendly relationships with such evil doers by overlooking their sins are their enemies. Those who are kind enough to try to correct them are the upholders of the True Dharma and true disciples of the Buddha. To prevent a friend from committing evil is really a friendly act. Therefore, one who accuses those of harming Buddhism is the Buddha’s disciple; and one who does not purge evil doers is an enemy of Buddhism.”

Kaimoku-shō, Open Your Eyes to the Lotus Teaching, Writings of Nichiren Shōnin, Doctrine 2, Page 113