Imamate Of 12th Differs From Imams # 1,2 and 3

[Rationalist]

In his last post the 12er Shia brother said...

When the Mahdi arrives, this shubha will be lifted as the mukhalifeen will have no choice but to believe - because he will be there calling to himself and to the true Islam. If they reject, they will be regarded as kafir in both dunya and akhira, as opposed to only akhira, as some scholars have stated.


Can you tell me why the Imams you number1,2 and 3 didn't enforce this condition? Where they hide the full true Islam?


Also you said

What is meant by shubha is that you are not intentionally rejecting a part of the revelation (e.g Imamah) - but that this particular aqeeda has not been proven to you.  And so, when the Mahdi (as) returns, there is no room for doubt because he will prove this to you.


For the 12ers reports such as Khutbah Shiqshiqiyah, Fadak, Saqifa are proofs for Imamate.
We know that in his Caliphate Imam Ali (as) released the sermon Shiqshiqyah, but the people of Kufa still remained close to aqeeda of the Bakris. Can you tell me if the first 3 Imams supported non-Muslims? Did they become non-Muslims after Khutbah Shiqshiyah?
Why do the first 3 Imams still want to become the leaders of people closer to the Bakris, yet the last Imams has no room for it?