Iran is not a democracy, but its system, which combines unelected religious authority with a subordinate elected civilian one, was designed to give people a chance to let off steam from time to time within carefully set electoral limits.
Out of the 46 million Americans with no religious affiliation, 13 millions are self-described atheists and agnostics, but another 33 million are people who ascribe to some faith just not to any house of worship.
The BBC's Zaffar Abbas in Islamabad says Karachi in particular has a long history of religious and ethnic violence, but the month of May was the worst in recent years - with more than 50 people killed in different incidents of violence.