A: Yes, some scholars are of this view. Although, no clear text concerning this matter is stated, it constitutes one of the major obligations in Islam.
The Pillars of Islam specified by Prophet Muhammad (peace be upon him) are five. He (peace be upon him) stated, "Islam is built on five (Pillars): the testimony that there is no god except Allah and that Muhammad is the Messenger of Allah; establishing Salah (prayers); paying Zakah (obligatory charity); fasting Ramadan; and Hajj (pilgrimage) to the House (the Ka'bah)." (Agreed upon by AlBukhari and Muslim)
Thus, the Prophet (peace be upon him) pointed out the pillars and fundamentals of Islam. It is impermissible to add an additional pillar, unless there is valid textual evidence. However, enjoining good and forbidding evil is one of the fundamentals and obligations in Islam, but it must not be stated as the sixth pillar due to the lack of the evidence.
Similarly, Jihad (fighting/striving in the Cause of Allah) as well as abstention from Haram (forbidden) things are fundamentals of faith, but they must not be stated as two of the Pillars of Islam due to the lack of the evidence.