Re: original shia part 2
pcg, im still unsure as to what you consider acceptable basis. if you consider it to be just the Quran and not hadees, then you’re taking yourself out of the sunni daira, and into the much maligned (by sunnis and shias 
) segment of ahl e quran (?) . one example of how few in number such people are is that out of all the posters on gupshup, only pakistaniAbroad would agree with your perspective on things. not that that automatically makes you wrong, it just takes you out of the shia-sunni debate and into the sunni-ahl e quran-shia debate which is a whole different ballgame.
if you wish to use the sunni basis for fiqh (Quran AND hadees) I believe the source of the Caliph remaining in the Qureish is traced to a hadees, a sahih hadees the narrator of which was one of the first three khalifas. I am not sure but I think its the 1st caliph.
I disagree with this hadees too, and I agree when you say that all people are spiritually equal in the eyes of Allah. You repeatedly characterise the shia view of rule as hereditary, as I said, it isnt hereditary in our eyes, just as the Abrahimic lineage of Prophets wasnt hereditary as you would define it. That said, there is precedent in Islam of one tribe or one family (Hazrat Ibrahim’s) having a higher proportion of Prophets, that does not mean that men and women and tribes were unequal in the eyes of Allah before He changed His mind after the revelation of Islam.
So each of our imams attained imamate and his status of infallibility through virtue and his own deeds and not through a divine purification. that is my view, there is difference of opinion on this in shias too, i believe.
as for the debate on the meaning of mawla, there was one on GS, but I wasnt able to locate it, its lost in the many different ones that have occurred over time. I will give you a wahabi “refutation” of the ghadeer event though. i hate to give this site though, because this site is famous in shia circles for its revisionist view of history. however this is the only sunni essay on ghadeer that I am aware of.
http://www.ansar.org/english/gadeer.htm
for balance, here is a shia version: