Chaltahai ji,
Here is my humble opinion on this issue:
For Muslims, religion is the WAY OF LIFE, not something separated from their lives that they just indulge in for a couple of hours. Religion does involve politics for us, there is no separation between politics and religion, or any sphere of life and religion. There is an Islamic way to do everything, including conducting politics. Religious gatherings can be and should be about everything under the sun.
The masjid-al-Nabwi, the first masjid ever built, that the Prophet Mohammad (peace be upon him) built in Madina served not just as a place of worship but as a community center for the Muslims in the city of Madina.
Islam has rules for every aspect of life at every level, including the way the world should be run, and ppl should be governed.
To remain silent towards oppression is a bigger aggression.
The imams did what was the need of the time. Their sermon does not need to be exclusively spiritual. Islam is a very wordly religion, and ofcourse their sermon should involve the most burning current affairs issue which is on the mind of every Muslim. It is the duty of the religious leaders of the community to keep the community informed abt Islam's viewpoint on all aspects of life, spiritual, social, political etc...
The rioting was very unfortunate but I am sure the imams did not tell the ppl to riot; that happenned because emotions were running high. I too condemn imams who preach violence, but it is a misconception that the majority do. There was rioting in anti war protests even in US cities today, and these ppl were non Muslims. I know non Muslims where I live in the USA were arrested for rioting.
Ofcourse the imams will remind the Muslims abt the Islamic duty of the ummah at this crucial time, at the Friday sermon. Muslims must not sit silently and witness this genocide and cruelty that is happenning in Iraq. The aim of the sermons was not to 'stir political and sectarian passions' but to make people realise that what was going on in Iraq is CRUEL and UNJUST.
The Prophet Mohammad (peace be upon him) said , 'Whosoever from among you witnesses evil, he should change it with his hands. And if he is unable to do so then he should change it with his tongue. And if he is unable to do so with his tongue, then he should at least consider it to be wrong. And this is the weakest stage of Imaan.'