hazrat li (ra) once had a fight with hazrat fatima (ra)....
shud we curse him for that????
and the hadith shiaas love to bring up "whoever makes fatima angry makes me angry" was actually directed towards hazrat ali (ra) when he wished to marry the daughter of an enemy of Allah and His Prophet which made hazrat fatima (ra) angry....
muawiya (ra) and ali (ra) were both companions of the prophet....
yes, ali (ra) holds a much higher status than muawiyah (ra) but if they had a dispute on a matter, it doesnt mean u start hating muawiyah (ra) and cursing him....
and we all know muawiyah (ra) was at wrong to have fought against ali (ra) but then he had reasons....
and perhaps hassan (ra) set us a good example of disclaiming the right to khilafa to avoid more bloodshed amongst muslims, thus giving more light to the prophet's saying about him "this son of mine is a sayyad (leader) and he will bring peace to two groups of muslims"....