Jeffrey Weiss of Real Clear Religion says the question Is Islam a Religion of Peace is a nonsense question.
There are about a billion people on this planet who say they are Muslims. They are split into about as many sects and sub-sects as Christianity. With deep and dividing disputes between those sects that make little sense from the outside. (Nothing special about Islam in that. Seriously: filioque?)
And the vast, vast majority of them live their lives without engaging in a scintilla of faith-inspired violence. In fact, many say their faith inspires acts of charity and generosity. Based on the evidence, therefore, the only correct answer to the question "Is Islam a religion of peace?" is: "It can be."
This is only a disputable answer if you define Islam per se to exclude the hundreds of millions of self-professed Muslims who live peacefully. Which seems not a particularly honest or useful approach.
So the more interesting question is: How can Islam be a religion of peace? And the way to get an answer is to find Muslims who live peacefully and ask them how it works.