Nobody wants to be ridiculed. Plenty of experiments have shown that people are willing to sacrifice their own time or money to punish people they thought treated them with lack of appropriate respect.
These feelings of disrespect are deeply embedded in the human psyche. When you and I cannot share moral sentiments or fellow feelings, then, according to Adam Smith
We become intolerable to one another. I can neither support your company, nor you mine. You are confounded at my violence and passion, and I am enraged at your cold insensibility and want of feeling. (Theory of Moral Sentiments)
It’s thus no surprise that young males (typically) vent their anger, sometimes uncontrollably with random and spontaneous acts of violence.
The extremist attacks in France and elsewhere are far more sinister, because they are not the irrational display of instinct, they are the logically planned and premeditated assassination of people with whom you disagree.
Recall that Adam Smith’s moral theory is based on human instincts, but he never says one’s actions should immediately respond to one’s instincts (such as for revenge). Rather, one’s actions should be guided by self control and by obeying the rules and laws of society. The laws typically preclude murder and unprovoked attacks.
It is not sufficient to say that I was insulted, so therefore I have the right to retaliate.
The argument that the laws of Islam support the murder of blasphemers is wrong and maliciously so. See the carefully reasoned and supported argument here on this issue.
The extremists who murdered in the name of Mohammed use a religious excuse to carry out what is decidedly a political agenda.