When does Free Speech morph into Blasphemy?

GoPetition hosts many causes of a religious nature. Conversely, many petitions at GoPetition promote the notion of free speech, often at the expense of religious sensibilities. These competing claims of religious freedom and free speech were recently highlighted at GoPetition in an "anti-protest protest" surrounding the controversial "Everybody Draw Mohammad Day".
Everybody Draw Mohammed Day is ostensibly a protest against Islamists who threaten violence against individuals who attempt to depict Muhammad. It originally began as a protest against censorship of South Park episode "201" by Comedy Central in response to death threats from radical Islamists. It started with a drawing posted on the Internet on April 20, 2010, suggesting everybody create a drawing representing Muhammad, a prophet of Islam, on May 20, 2010, as a protest against Islamist efforts to limit freedom of speech. The protest became a focus for a variety of Facebook (FB) members.
According to Wikipedia, U.S. cartoonist Molly Norris of Seattle, Washington, created the artwork in reaction to Internet death threats that had been made against cartoonists Trey Parker and Matt Stone for depicting Muhammad in an episode of South Park. Depictions of Muhammad are explicitly forbidden by a few hadith (Islamic texts), though not by the Qur'an. Postings on RevolutionMuslim.com had said that Parker and Stone could wind up like Theo van Gogh, a Dutch filmmaker who was brutally murdered and mutilated by a Muslim extremist. The individuals running the website later denied that the postings were actual threats, although they were widely perceived as such. Norris said that if millions of people draw pictures of Muhammad, Islamist terrorists would not be able to murder them all, and threats to do so would become unrealistic.
Campaigner, Ali Asadullah Baig, reponded to the proposed "Day" with his own petition campaign at GoPetition. He wanted the event stopped. As one Pakistani supporter, Sobia Makhdoom, commented in support of the internet petition, "I can only say that being civilised humans, 'they' should also respect our Prophet S.A.W.W, religion, as we respect Isa (Jesus) A.S. or Dawood (David) A.S. as our early prophets."
Ali Baig's complaint against "Everybody Draw Mohammed Day" is not isolated. Many have complained. Law professor and blogger Ann Althouse rejected the idea because "depictions of Muhammad offend millions of Muslims who are no part of the violent threats." James Taranto, writing in the "Best of the Web Today" column at The Wall Street Journal, also objected to the idea, not only because depicting Mohammed "is inconsiderate of the sensibilities of others", but also because "it defines those others—Muslims—as being outside of our culture, unworthy of the courtesy we readily accord to insiders." Bill Walsh of Bedford Minuteman wrote critically of the idea: "Although it’s clever, it’s also an 'in your face' reaction to the prohibition against drawing the holy figure." 
Writing for The American Spectator, Jeremy Lott commented positively about the protest movement: "While the suits at Comedy Central and Yale University Press have been cowed, people across the country have decided to speak up and thereby magnify the offense a thousandfold." Helge Rønning, a professor at the Institute of Media and Communication at the University of Oslo, said the offense to Muslims was outweighed by freedom-of-speech concerns. "Indignation from those who claim the right to engage in criticism of religion is as important as the indignation that comes from the Muslim side," he told the NRK (Norwegian Broadcasting Corporation). "I think that this is an attitude that goes deeper than whether these drawings are blasphemous or not." Vebjørn Selbekk, a Norwegian editor who was threatened in 2006 after he reprinted Danish cartoons of Mohammed in his publication, supported the May 20 protest. "I think maybe this is the right way to react—with humor, and also to spread this number, so it isn't only a few who sit with all the threats and all the discomfort associated with defending our freedom of speech in this area," he said.  
In an analysis of the protest movement and surrounding controversy, staff writer Liliana Segura of AlterNet noted, "In a democratic society where free speech is vigilantly protected, it is perfectly reasonable to call out censorship, particularly when it springs from some form of tyrannical religious extremism."
Whichever way this debate is sliced, there seems to be a tolerance differential developing in Western Societies. While parodies of Christ and Christians virtually go unnoticed in the Press and social media, parodies of Mohammed and Islam do not. Why? Is Christianity a more tolerant religion in itself? More prone to "turning the other cheek" at offence? Or have Christians become complacent about their faith? 
Knowing when a petition, or "free speech" crosses the line and morphs into blasphemy is a tricky question. One which won't be resolved here. However, at the end of the day, mutual respect and sensitivity will go a long way in averting major conflicts between those with radically different views.