Zaidi View on Al Mamoon Rasheed

Thank you for your points! However, the original question asked about the Zaidi view of al-Mamun. I provided numerous Zaidi references substantiating our claim that he poisoned Imam Ali b. Musa ar-Rida (as) as well as other atrocities.

I'm sure that there are references in Sunni works which seek to exonerate al-Mamun of the things he did. Maybe he was a bit easier on the Alids than his forebears, especially the accursed Harun ar-Rasheed. However, the Alids posed a threat to Abbasid political authority as they were rivals for the throne. Previous Alid rebellions under the Abbasids created a need for the Banu Abbas to either continue their brutal suppression of them or to seek a more subtle means to appeal to Alid supporters. If they continued physical aggression against the Alawis, it would no doubt foment anti-Abbasid sentiment among the people just as the Umayyads previously. It would therefore make sense to apparently appoint an Alid as a successor because it would undermine any attempts from Alids or their supporters to revolt. Sure, it may cause problems with the prevailing Abbassid idea but politically, it served its purpose of preventing Alid revolution on principle. It was rather brilliant from a dunyawi political perspective.

As for al-Mamun reversing the judgement of Fadak and other seemingly pro-Alawi policies, as you said, the Abbasids were for all intents and purposes "Shia" in that they believed in the exclusive right of the Prophet's relatives. So, it would make sense that he would promote "Shia" interests without favouring Ali (as) over Abbas.

And Allah knows best!

IRS