The opponents debate endlessly with the Shias on the matter of caliphate and claim the caliphs were most deserving of the position, which they had actually usurped. They ignore all arguments and references to the contrary.
Here is an interesting debate on caliphate and how even Iblis was more deserving of caliphate than the so-called knowledgeable caliphs.
Abul Hasan Ali b. Maytham (i.e. the son of Maytham al-Tammaar) asked Abu al-Huzail al-Allaaf (a leading Mutazilah scholar): Is it true that Iblis prevents one from doing all good deeds and commands one to commit all evil deeds?
Abu Huzail: Yes, indeed it is so.
Ali b. Maytham: O Abu Huzail, is Iblis aware of all the good deeds and prevents one from committing them and is he aware of all the evil deeds and commands one to do them?
Abu Huzail: Yes, he is aware of it.
Ali b. Maytham: Is the one whom you consider as an Imam (Abu Bakr) after the Holy Prophet (s.a.w.a.) aware of all the good and evil deeds?
Abu Huzail: No
Ali b. Maytham: Then Iblis is more knowledgeable than the person you consider as your Imam.
Abu Huzail was stunned and couldn’t utter anything; because a person having more knowledge is more honorable than the one with lesser knowledge. Accordingly, Iblis is superior and more honorable when compared to Abu Bakr.
(Al-Fusool al-Mukhtarah pg 23, Al-Ehtejaaj vol 2 pg 150 footnote)