A Secret Agenda

Taqiyya is a practice that God Permitted to Muslims living in aggressively Anti-Muslim Lands to allow Muslims to continue professing their faith in secret. It was practiced by Muslims stranded in Pagan-Makka who were unable to join their fellow believers either in Abyssinia or Madina, though Spanish Muslims also practiced this from 1493CE until recently [1].

I would propose that Banu Hashim were never actually interested in Islam and when they were hit by The Boycott [2, 3], this simply embittered them against both Islam and their fellow Al-Quraish. They would later practice Taqiyya would create the impression they embraced Islam, but really they were looking for an opportunity to strike back. After Muslims conquered Persia, the Hashemites packed their bags and emigrated to these new lands, slowly brainwashing the Persians into believing they were victims of their fellow Tribes-People.

When [the Politically-Sensitive] Uthman succeeded Umar Al-Khattab, the Hashemites saw this as an opportunity to create fitna and fassad by claiming the Ummayyads were obsessed with Power and preventing anyone else obtaining Seats of Authority. These would ultimately culminate the Political Crisis resulting in Assassination of Caliph Uthman and a succession of devastating wars [3] climaxing in the Battle of Siffin.

I would also propose that later on Banu Hashim (specifically the Sharifs[5] ) would encourage their Tribal Cousins the Abbasids (descendants of ibn Abbas [7,8]) to unite the Persians and overthrow the Ummayads [6], hoping they in turn would use their 'influence' over a united Persian Army to rebel against the Abbasids and instil them as leaders.

After the Abbasids overthrew the Umayyads, they discovered the Banu Hasim plot to overthrow them and started oppressing the latter. This would lead to the Banu Hashim 'going underground' and creating an entirely new type of Military Discipline: 'The Assassin' [9, 10]. I'm not sure how they ended up ruling Western Hijaz(967CE-1201CE) or Makka(1201CE-1925CE) respectively [11] but according to the book ibn Battuta's Travels (by HAR Gibb[17]) they seemed to wield considerable influence over the Mongols post-Apocalypse (the Mongol-Templar Alliance that destroyed much of the Muslim World between 1233 and 1300 [12, 13, 14, 15, 16, 17]).

Also judging by the way they led the Arab Apostacy against the Othmani Khilafat, I would suggest that Banu Hashim's SOLE interest in life is Power.

Much of this is pure speculation simply because there is very little substantial evidence. However I do believe there was a Hashemite(Sharif)-Mongol-Templar Conspiracy that led to the near total obliteration [of the Muslim World], which I based on two fundamental questions:

1. Why did Hashemite(Sharif) Ruled-Makka survive the Mongol onslaught [unscathed], when they obliterated every other city they encountered?
2. Having destroyed each city and peoples, the Mongols reduced the survivors to a lifetime of barbaric slavery and servitude, except the Hashemites [who seemed to enjoy a great deal of 'favour' from the Mongols]. Why would the Mongols choose to provide special favour to the Hashemites?

Available evidence aside one thing is VERY clear. The Crusaders (irrespective of how they were represented ie Templars etc) were ALWAYS a bunch of arrogant mass-murdering bastards whose ONLY purpose in life was to kill, kill and...kill and they would ultimately lay the foundations for...the Nazis (I see NO difference between the Crusaders and The Nazis...well the former are hailed and the latter are reviled).

References:
1. http://www.secularism.org.uk/spanishanti-islamfestivaltoneddo.html
2. http://www.witness-pioneer.org/vil/Articles/companion/06_ali_bin_talib.htm
3. http://en.wikipedia.org/wiki/Meccan_boycott_of_the_Hashemites
4. http://en.wikipedia.org/wiki/Muawiyah_I
5. http://www.kinghussein.gov.jo/hash_intro.html
6. http://en.wikipedia.org/wiki/Umayyad
7. http://www.pakistanlink.com/Commentary/2006/Sep06/02/03.HTM
8. http://en.wikipedia.org/wiki/Abdullah_ibn_Abbas
9. http://www.skewsme.com/assassin.html
10. http://en.wikipedia.org/wiki/Hashshashin
11. http://www.kinghussein.gov.jo/hash_intro.html
12. http://en.wikipedia.org/wiki/Wikipedia:Featured_article_candidates/Franco-Mongol_alliance/archive1
13. http://www.countyhistorian.com/cecilweb/index.php/Franco-Mongol_alliance#Early_contacts_.281209-1244.29
14. http://en.wikipedia.org/wiki/User_talk:Elonka/Archive_10
15.http://www.historyofjihad.org/crusades.html
16. http://en.wikipedia.org/wiki/Franco-Mongol_alliance
17. http://en.wikipedia.org/wiki/Ibn_Battuta