First of all what is Imamah or Shia Imamah? Lets take a look at this first. Shia Imamah is continuous divine guidance after Nabuwwah which is also divine guidance. The Qur'an and Sunnah wasn't left unattended and the Muslim Ummah wasn't left without a divine guide. Nabuwwah had to do with mankind where as Imamah after it doesn't have to do with mankind but has to do with the Muslim Ummah. There is a clear difference.
Now this is an internal matter that certain individuals weren't happy with the divine concept of Imamah and they did all they could to follow their own desire and plans.
Guidance after the Nabuwwah was/is through the scholars, because the ruling and knowledge of every matter is already in the Quran and Sunnah.
العيون: بالاسانيد الثلاثة عن الرضاء عن ابائه عليهم السلام: قال رسول الله صلى الله عليه واله: اللهم ارحم خلفائي- ثلاث مرات – قيل له ومن خلفائك قال الذين يأتون من بعدي ويروون أحاديثي وسنتي فيعلمونها الناس من بعدي
al-Uyun: Via the three chains from al-Ridha from his forefathers عليهم السلام: the messenger of Allāh صلى الله عليه واله said: O Allāh have mercy on my successors – thrice – it was said to him:
and who are your successors? He said: those who come after me and transmit my narrations and my Sunnah teaching it to the people after me. الكافي: عدة من أصحابنا، عن أحمد بن عيسى، عن أحمد بن محمد بن أبي نصر عن أبان بن عثمان، عن ابن أبي يعفور، عن أبي عبدالله عليه السلام أن رسول الله صلى الله عليه وآله خطب الناس في مسجد الخيف فقال: نضر الله عبدا سمع مقالتي فوعاها وحفظها وبلغها من لم يسمعها، فرب حامل فقه غير فقيه ورب حامل فقه إلى من هو أفقه منه …
al-Kafi: A number of our companions from Ahmad b. Muhammad b. Isa from Ahmad b. Muhammad b. Abi Nasr from Aban b. Uthman from Ibn Abi Ya’fur from Abi Abdillah عليه السلام who said: the messenger of Allah صلى الله عليه وآله gave a speech to the people in the Masjid of al-Khif and said:
may Allah make radiant [the face of] a slave who hears my words and understands them and memorizes them and relays them to the one who did not hear them, for it may happen that a bearer of Fiqh is not a Faqih and it may happen that a bearer of Fiqh relays them to one who is more of a Faqih than him …
الكافي: عدة من أصحابنا، عن أحمد بن محمد بن خالد، عن إسماعيل بن مهران، عن سيف بن عميرة، عن أبي المغرا، عن سماعة، عن أبي الحسن موسى عليه السلام قال: قلت له: أكل شئ
في كتاب الله وسنة نبيه صلى اليه عليه وآله؟ أو تقولون فيه؟ قال: بل كل شئ في كتاب الله وسنة نبيه صلى الله عليه وآله
al-Kafi: A number of our companions from Ahmad b. Muhammad b. Khalid from Ismail b. Mihran from Sayf b. ‘Amira from Abi al-Maghra from Sama’a from Abi al-Hasan Musa عليه السلام, he said:
I said to him: is everything in the book of Allāh and the Sunnah of his prophet صلى الله عليه وآله or do you have a say in it? he said: rather everything is in the book of Allāh and the Sunnahof the prophet صلى الله عليه وآلهAnd this can not be the guidance. Even the narrator could not bear the pain.
علل الشرائع: أبي، عن سعد، عن محمد بن الوليد والسندي، عن أبان بن عثمان، عن محمد بن بشير وحريز، عن أبي عبد الله عليه السلام قال: قلت له: إنه ليس شئ أشد علي من اختلاف أصحابنا، قال: ذلك من قبلي
Ilal al-Sharai: My father from Sa’d from Muhammad b. al-Walid and al-Sindi from Aban b. Uthman from Muhammad b. Bashir and Hariz from Abi Abdillah عليه السلام,
he (Hariz) said: I said to him: there is nothing more difficult for me [to bear] than the differences [that exists] between our fellows, he said: that is from me (I purposely caused that).It was clear that the Prophet s.a.w asked for pen and paper and they weren't interested. They had the book of Allah with them and they believed it was sufficient for them. So this wasn't a matter for Muhammad s.a.w to impose by force. Nor was it a matter for Ali ibn Abi Talib or other Imams to fight for. It was something the Prophet s.a.w wanted for the the benefit of the Ummah. And if certain people aren't interested, they don't think it's necessary and have their own idea and plans then 'La ikraha fideen" their is no compulsion within religion.
Is it possible that Allah (swt) and His Messenger (s.a.w.w) would stop and not complete the revelation/order just because certain people are not interested? Remember 5:69 (Shia version of Gadhir).
At the end of the day this isn't an external matter regarding shirk or kufr. But infact it's an internal matter of the Muslim Ummah which is sensitive and delicate. That's why it was dealt with patience and tolerance rather than the sword and by heavy handed tactics.
So, basically you’re trying to say that the tactics of Zayd bin Ali (as) and his likes from ahlul bayt were not right. But on other hand we have reports about his martyrdom from Prophet (s.a.w.w) and about his resemblance to Ali ibn Abi Talib (as) more than any other member of ahlu bayt at that time. May be that was the reason, why many scholars/fuqha as well (not just laymen) supported his revolt against tyrants.
Plus I've already mentioned that those who got into authority and gained power used what ever means necessary to restrain members of the Ahle Baith, their family, friends and supporters via persecution.
This is not true at least for the supposed divine Imams.
Sheikh Mufeed says:
Chapter: As for what Abu Ja‘far mentions of the death of our Prophet and the Imams by poison or murder, some of this is confirmed as fact and some not. What is confirmed is that the Commander of the Believers, al-Hasan and al-Husayn, peace be upon them, departed from this world by murder, none of them died a natural death. Musa ibn Ja‘far, peace be upon him, was killed by poison.
It is highly probable that ar-Rida (‘Ali ibn Musa) was poisoned, yet this cannot be confirmed. As for the others, there is no justification for the claim that they were either poisoned or murdered or killed through persecution, since the reports concerning this matter are extremely confused, and there are no means of proving it definitely.