Who has the responsibility for proving Islam is a 'religion of peace'?

Al Colby sent me this picture.  And as the phrase goes:  it says a thousand words.  Many of them unfair, of course.  But it raises a question that Muslims have never really been required to answer: Given the level of violence and cruelty committed in the name of Islam, why should non-Muslims assume otherwise?  The argument that Islam is a religion of peace is one that Muslims must make every day to counteract the cruelties committed so often and visibly by their co-religionists.  We Christians have been analyzing, apologizing and explaining for centuries the sins done in our name.  So should Muslims.  Sauce, Goose, Gander.