However...
However, he rebelled as a mutineer and a protestor during Imam ‘Ali’s (‘a) time as caliph, under the slogan of not accepting ‘Ali’s regency, he claimed that ‘Ali had given shelter to ‘Uthman’s killers and that ‘Ali himself was involved in the assassination of the true caliph of the Muslims; therefore, he could not be the rightful caliph.
As such, Mu‘awiyah rebelled as a protestor in a group of protestors under the same slogana combat against a government that was not lawfully established and whose leader has blood on his hands. Up to then, he never claimed vice regency and people had not started referring to him as the Commander of the Faithful. He would just claim that they were a group of people who did not wish to obey the government. Imam al-Hassan takes the position of vice-regent after Imam ‘Ali.
Mu‘awiyah became more powerful day by day. Due to specific historical reasons the circumstances of Imam ‘Ali’s government, that Imam al-Hassan later inherited, was being weakened from within. It has been written, that 18 days after ‘Ali’s martyrdom, Mu‘awiyah leaves to conquer Iraq (these eighteen days include the time it took for the news to spread as far as Damascus and Mu‘awiyah’s announcement for public preparation and mobilization of an army).
Here, Imam al-Hassan is in a particular situation: he is the caliph of Muslims and a rebellion has risen against him. Imam al-Hassan’s murder in this situation would mean the murder of the caliph of the Muslims and defeat of the core of the caliphate. Imam al-Hassan’s resistance to the point of getting killed was similar to that of ‘Uthman during his time. However, it was not similar to Imam al-Husayn’s resistance.
Imam al-Husayn’s situation was a situation of protest against the ruling government.1 If he would get killed (which he did), his death would be an honorable one, which in fact became so. He objected to the situation, the government of the time and the spread of corruption. He believed that they did not qualify for the task and during the passed twenty years they proved what kind of people they really were. He remained persistent upon his word until the very end.
For this reason, specifically, his uprising was and continues to be considered honorable and courageous. Form this point of view, the circumstances of Imam al-Hassan are exactly contrary to those of Imam al-Husayn: he was someone who was placed in the position of governor who faced objections from an opposition.