Regardless of Islam's past and the words of the Quran and Muhammed's actual life, most Muslims are evolving their religion toward a peaceful one and reconfiguring their history (as all religions do) to make it work in the modern world. Unfortunately, like Senax says, the radicals get more TV time not just here but in centrally controlled Middle Eastern TV. THe perceived power of the radicals makes their power, in effect, real. Those who should be speaking against them find themselves torn for many reasons:
fear of radicals killing their families, fear of possibly irking their God by going against clerics (especially in ME countries with controlled TV programming where only radical clerics are heard and the bulk of the population is uneducated), the suspicion that Westerners will not listen and will hate them anyway (as reaffirmed by our general reaction, especially in intolerant European countries- cough France cough cough)... probably even an idea that it should be obvious most Muslims are not violent. Afterall I'd imagine a nonviolent Muslim in a nice Western area (as opposed to a slum) meets peaceful Muslims on a regular basis and assumes it should be obvious (no group has a monopoly on self-centered ignorance- we all have it to some extent).
It's pretty clear that France's problem is due to its intolerance and failure to integrate. Even in other European countries where such problems exist, it is not as bad by any extent. In the US such problems are nearly unheard of.

As for whether Muslims should speak up against their radicals... of course they should. But how can they when they're always on the defensive from the people who should be backing up those denouncements?
What we're more likely to hear is a denouncement of both the West and radical Islam.

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"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside