Nichiren’s Tendai contemporaries … held the Lotus Sutra to be all inclusive, but generally took this to mean that, properly understood, any practice, such as chanting Amida Buddha’s name or invoking the Bodhisattva Kannon, could be considered practice of the Lotus Sutra. Nichiren decried this interpretation as a confusion of the true and the provisional and rejected all other, “pre-Lotus Sutra” teachings as no longer suited to the present time of mappō. Like medicine that stands too long on the shelf and becomes poisonous, these other teachings and the practices based upon them were, in his view, not only soteriologically useless but positively harmful. For Nichiren, to willfully set aside or ignore the Lotus in favor of other, “lesser” teachings amounted to “slander of the Dharma” and would pull the practitioner down into the lower realms of rebirth.

He therefore taught his followers that one should not only embrace faith in the Lotus Sutra oneself, but spread that faith to others, assertively rebuking adherence to other, provisional teachings. This is known as shakubuku, the “harsh method” of propagating the Dharma by actively challenging “wrong views.” Nichiren saw shakubuku as compassionate action that would enable others to form a connection with the Lotus Sutra and save them from both misfortune in this world and rebirth in the evil realms.
A Buddhist Kaleidoscope; Jacqueline I. Stone, When Disobedience Is Filial and Resistance is Loyal: The Lotus Sutra and Social Obligations in the Medieval Nichiren Tradition, Page 264