As to the first,PA did respond in defence which is the maximum allowed. Allah knows better but let him be the judge between the killer and the killed muslim. Also your logic regarding following the khalifa blindly makes Hussain RA culpable and also Abdullah ibn Zubair RA culpable as they both took up arms against the established khalifa. What do you say to that?
As to Hussain RA,a lot of sahaba including ibn Umar RA, Abdullah ibn ZubairRA, and even Ibn AbbasRA advised him against the journey to kufa. The later came all the way from Madinah to talk to him. You should find the time to go and read about their conversation to educate yourself as it is recorded in history and is an amazing insight into the iman of the Sahaba and the sagacity of Ibn Abbas RA. The fact that Hussain RA chose to follow his iman is upto his own ijtehad and Allah knows best. I am not worth the dust of the feet of ibn Ali RA who is one of my fore fathers to be able to comment.
The fact still remains that the matter is a unsavoury one and one should not deride a fellow muslim no matter how misguided. PAdid just enough to defend itself and its conduct falls within the rights of self defence which it is allowed to. Incidentally Hussain RA was not the only member of Ahle bait who fellprey to the treachery of the people of Kufaa. One of his grand children Rahimahu Allah tried as well( I forget the name) to stir a mutiny with the help of the Kufans was betrayed just like Hussain RA and brytally murdered. Abdullah ibn Abbas RA was also killed in Madina by Hajjaj in a most brutal manner and this incidence and the farce that went on with it is one of the blackest chapter in the history of early islam.
A
Imam Hussein R.A never started his journey with the intent to fight yazeed He was invited by the kufans neither did they took arms------ until after the the incident of Karbala happened
2nd no Muslim is allowed to raise weapons against the Muslim caliph until or unless he overtly put a ban on any of the 5 Pillars of Islam and this criteria fits on yazeed
3rd yazeed was made king in violation of the treaty between Caliph Hassan and Muaveyah
Regarding that part of your post that I should read yazewd is a khalifa naozbILLAH he was a tyrant king sultan whatever but not a caliph under any interpretation of Islamic Traditions
As per The Hadith Imam Hassan R.A was the Last of the Caliphs
: The Prophet (peace be upon him) said, The Caliphate will remain after me for thirty years, then it will change into a cruel monarchy. Thus, Mu`awiyah said after thirty years had passed, "I am the first of the kings."
(Extracted from the treatise written by Abu Zayd Al-Qayrawany, vol. 1, p. 96).
What is the interpretation of this Hadith?
A: This Hadith was related by Imam Ahmad in "Al-Musnad", Al-Hakim in "Al-Mustadrak", Abu Ya'ly in "Al-Musnad", ibn Hibban in his Sahih (authentic) Book of Hadith, and Al-Tirmidhy in his " (Sunan).
One of his grand children Rahimahu Allah tried as well( I forget the name) to stir a mutiny
Hazrat Zaid ibn Ali
P.S its not a Sunni forte to chant katil bhi raziAllah or maktool b RaziAllah