salam.
i would like the thoughts of all of you here. if sunnis see it as perfectly reasonable to establish beliefs based on sunni hadiths, then why can't a shia establish beliefs based on shia hadiths? for example, the belief in twelve infallible imams. i'm convinced from the other thread i recently made that the concept cannot be proven through sunni hadiths as many shias have claimed. however, this doctrine is clearly reported in shia literature and hadiths. so what's the problem if someone uses a hadith from usul al kafi or other collection which is graded as sahih according to shia scholars?
Brother the fact is that, Shias establish their beliefs based on their hadeeth, and likewise Sunnis establish on their own hadeeth. Now as per Sunni standards of Hadeeth science, Jarh wa Tadeel of narrators, the Shia hadeeths are unreliable. The Shias would give you the same reply about Sunni hadeeths.
So an independent researcher needs to make a comparative study about the details and differences between the Hadeeth science of Shias and Sunnis. The effort each sect put, in regards to gather the information about narrators from whom they took their deen, focusing on the defects in pattern of transmission etc. And if you do that, you would fairly reach the conclusion that Sunnis surpassed Shias in this field. So taking opinion of Shia Schlars regards Hadeeth sciences is much safer and logical.
But, obviously its not possible for every random individual to take up this task and complete it in a proper manner. So you need to look at things from a different perspective. For example, as the brother pointed out, you need to find explicit evidences from Quran which support the fundamental of Shia creed(Imamah after Prophet). You'll realize that their isn't any clear evidence, what all that is brought is ambiguous. Infact their are verses which go against Imamah , like 4:59.
Most importantly, the historical fact that there were so many different Shia sects in regards to believing in the number of Imams. You can read about them in Shia books like Firaq al Shia. Or on articles on twelvershia website. If the number of Imams were known then Shias wouldn't have differed so much, there wouldn't have been, seveners like waqifis, etc.
There wouldn't have been a need for attributing Bada to Allah in regards to Imamah after the death of sons of Imams.
Lastly, Shia scholar of Hadith Muhammad Baqir al-Behbudi writes in "Ma`rifat al-Hadith" pg.172:
على انك عرفت في بحث الشذوذ عن نظام الامامة ان الأحاديث المروية في النصوص على الأئمة جملة من خبر اللوح وغيره كلها مصنوعة في عهد الغيبة والحيرة وقبلها بقليل فلو كانت هذه النصوص المتوافرة موجوده عند الشيعة اللإمامية لما اختلفوا في معرفة الأئمة هذا الاختلاف الفاضح ولما وقعت الحيرة لأساطين المذهب واركان الحديث سنوات عديدة وكانوا في غنى ان يتسرعوا في تأليف الكتب في اثبات الغيبة وكشف الحيرة عن قلوب الامة بهذه الكثرة
[And you (reader) now know after the research on "al-Shudhudh `an Nizam al-Imamah" that the narrations about the general identity of the Imams such as the narration of the Tablet (1) and others, are all fabricated during the time of al-Ghaybah (2) and al-Hayrah (3) and some short time before it. For if these narrations were available with the Imami Shia, they would not have disagreed so openly and greatly about the identity of the Imams, nor would the biggest personalities and narrators of Hadith have faced much confusion for long years, nor would they have needed to quickly write books proving the Ghaybah to unveil the confusion from the hearts of the nation in such great numbers.]
Footnotes:
(1) Narrations of the Tablet are those when Jabir (ra) walks in on Fatima (ra) and sees a tablet with the names of the Imams on it.
(2) al-Ghaybah is the period of occultation of the Shia 12th Imam when he was never seen nor heard from by anyone except four people and only for a couple of years, then followed by the greater occultation.
(3) al-Hayrah is the great confusion that struck the followers of the Imami branch of Tashayyu` when the news of their Imam stopped reaching them after the death of the fourth emissary and lots of them abandoned the Madhab.