Such a claim involves truths, falsehoods, and delusions. The following is an elaborated explanation of that point:
His claim that "he does not deny that every Muslim should guide to the right, teach righteousness, and so on", is true and it is the duty of every one endowed with insight to undertake, for it is the way of our Prophet Muhammad (peace be upon him) and of those who followed him with sure knowledge.
Allah (Exalted be He) says, Say (O Muhammad ﺻﻠﻰ ﺍﷲ ﻋﻠﻴﻪ ﻭ ﺳﻠﻢ): "This is my way; I invite unto Allâh (i.e. to the Oneness of Allâh Islâmic Monotheism) with sure knowledge, I and whosoever follows me (also must invite others to Allâh i.e. to the Oneness of Allâh Islâmic Monotheism with sure knowledge).
This noble verse indicates that the true followers of the Prophet (peace be upon him) are those who follow him with sure knowledge and who call to the truth. Besides, Allah (Exalted be He) says, Invite (mankind, O Muhammad ﺻﻠﻰ ﺍﷲ ﻋﻠﻴﻪ ﻭ ﺳﻠﻢ) to the Way of your Lord (i.e. Islâm) with wisdom (i.e. with the Divine Revelation and the Qur'ân) and fair preaching, and argue with them in a way that is better.
Though the verse addresses the Prophet (peace be upon him), it generally applies to the whole Ummah, as Allah shows in it the way and levels of Da`wah (calling people to Islam). Thus, the Du`ah (callers to Islam, sing. Da`iyah) should undertake the call to Allah's Way strictly in the way outlined by Allah, whether the invited person is a believer or a disbeliever, with the exception of stubborn and wrongdoing ones (since proofs have already been indicated above about the permissibility of assuming harshness and strictness when treating such persons, within the limits of Islamic Shari`ah).
However, the writer claims that "A Muslim is not allowed to assume rigor or strictness in his sayings or deeds, since he is not authorized or entrusted by the authority entitled to do so. All that he can do is to repudiate what he sees as an evil from his heart, which is the least (form) of Faith for the one who is not in authority."
However, this is a superficial generalization and a manifest error as exposed through the preceding point, since all callers to Allah's Way, whether they are government officials or volunteers, are required to assume the Shar`i way in their Da`wah and they should avoid harshness and rigor in words and deeds, except when necessary as was indicated above. The writer's words, however, give the impression that the opposite is true.