The Rafida's argument is a logical fallacy based on wrong premises. Let me share with you guys this beautiful article that I found online:
Wasiyy وصِي
A spiritual legatee; inheritor; someone nominated to succeed in political and spiritual sense.
Primarily a word of Shi`as theology coinage, meaning those who were nominated to succeed a prominently spiritual authority. Their belief is that every Messenger left a legatee behind him and that the legatee (wasiyy) of Prophet Muahmmad was `Ali b. abi Talib; and that `Ali left a will that he should be succeeded by Hassan, and so on, until the twelfth Imam. In fact, Hassan b. Ali promptly withdrew from Imamah, in favour of Mu`awiyyah and to the applause of the Ahl al-Bayt, fulfilling a prophetic prediction.
However, history does not reveal that `Ali left any will in favor of Hassan as his successor; nor did the Prophet leave any will in favor of `Ali.
It is alleged that at the time of his death the Prophet asked for pen and paper (saying, “So that you will not be lost after me”), but the Companions prevented him from writing because they were afraid that `Ali would be nominated the successor (wasiyy). The report is correct, but the allegation that the Companions did not produce pen and paper because they feared `Ali’s nomination, is wrong. There are several problems in such a conclusion.
1. The Companions did not know that the Prophet was going to die in a few day’s time to infer that he wished to nominate someone.
2. The Prophet recovered, and was alive for several days. He could have got it written down by others. He had several secretaries writing Revelations for him.
3. He could have said the same thing to any of those around him, e.g., Fatimah, `Ali, `Abbas and others who were frequenting him.
4. The Prophet said something (in a report well-published by the Shi`as) to Fatimah in secret which made her cry and then smile. It was about her own death. Fatimah revealed this after his death. If `Ali had been nominated, Fatimah would have revealed it.
5. One of the easiest ways of nominating `Ali would have been to appoint him the Imam in Prayers. But the Prophet appointed Abu Bakr. He did not even agree with `Umar as the Imam.
6. In his last moments the Prophet spoke of things that concerned him most: women’s treatment, slaves’ welfare, importance of Prayers, not taking graves as places of worship (!) etc. Those were his last words, and things of first concern. But he never said anything, nor dropped a hint about `Ali’s succession.
7. Throughout his career, the Prophet never spoke of the concept of a necessary wasiyy of every renowned spiritual personality. In fact, he did not use the word “wasiyy” with the Shi`as concept in any Sahih hadith, but rather he said, “Scholars are the inheritors of Prophet.” If the concepts of wasiyy” and “ wasiyyah” hold central place in the scheme, the Prophet would have explained it in a most thorough fashion, as was his habit about important issues, and would not have left it for the Shi`as scholars to expound it several centuries after him.
8. The concept – treated as the central pillar of Shi`aism is missing from the Quran altogether, where we find Prophet Ya`qub (delivering the wasiyyah) enjoining his children to remain on Tawhid until death, and nothing else.
As regards the Hadith that the Prophet said to `Ali that ‘you are to me like Harun was to Musa,’ and the Shi`as inference that it means `Ali was the wasiyy, first of all, none of the Companions – not even `Ali - understood the words as meaning `Ali should be the first Khalifah after him, secondly, perhaps the majority of Shi`as do not know that Harun – the supposed wasiyy of Musa– died before Musa.
Some of the earliest Shi`as have gone to such extent to say that since `Ali did not claim the Khalifah during the reigns of Abu Bakr, `Umar and `Uthman, despite the Prophet’s instruction, he committed kufr, and broke away as sub-sects.
An Orientalists cleverly used the occasion to inject poison into the readers’ mind. Defining the term “WASI”, he wrote in the Brill Encyclopedia of Islam:
It was first used to designate `Ali as the inheritor of Muhammad’s worldly possessions (such as his books and weapons) and of his political and spiritual authority.
If someone points out the sneaky introduction of “books,” they would immediately say how sorry they are for the slip.