Author: Abdulhusayn Al-Musawi.
I personally have a nice and more precise point. When the Almighty applied the plural rather than the singular form as many do then those who hated `Ali as well as all those who were envious of and in competition with Banu Hashim would not be able to tolerate hearing it in the singular form for they would then be unable to hide the truth or water it down. Because of their desperation they might even do something quite harmful to Islam. It is quite possible that it was for this reason that the verse was revealed in the plural form though applied to the singular: in order to avoid the harm resulting from disgracing those folks.