Salam,
And what exactly makes you think that this was not out of necessity and compulsion because of the fact that people started to hate him (the Imam of the time!), and did it after 6 months of reluctance to accept it? Can you prove this from the Sahihain? Sahih bukhari: Volume 5, Book 59, Number 546 and Sahih Muslim:Book 019, Number 4352: are two entire ahadith about what happened, and they shows how the reason for Imam Ali (as) giving the oath of allegiance to Abu Bakr was that people started hating Imam Ali (as). Imam Ali (as), as the religious leader of his time, had to harness people’s favour in order to prevent them being mislead [since a person wouldn’t really obey a person a hates], which was ofcourse a political tactic in the form of Taqiyyah.
Read the above hadith from Sahih Bukhari. Why does the narrator ‘Aisha’] say Imam Ali (as) disliked Umar entering his house? Could it be, perhaps because he threatened to burn it? You want to accept that Imam Ali (as) would give his oath of allegiance to the same person who threatened to burn his house? Again, any proof from the Sahihain that he did give the oath of allegiance to Umar?
Oh, he did? Hmm… maybe that’s why, on the occasion of the Battle of Siffin, the issue that whether or not Uthman’s murder was just and should his murderers be punished or not, needed discussion? Last time I checked Imam Ali (as) was reluctant to accept that Uthman’s has justly ruled the Muslim Ummah and thereby held ‘talks’ to discuss it and come to a conclusion and act accordingly [widely known as the arbitration between Abu Musa al-Ashari and Amr bin al A’as].
Wa-alaykum Assalam