People have a very strange way of looking at Islam. I mean, it's not like people looked at the KKK and took them to be representative of all Christians, but for some reason people look at Al Qaeda et al and see them as representative of all Muslims. Shouldn't the hundreds of millions of perfectly normal, peaceful Muslims across the globe be testament enough that Islam is as peaceful a religion as any other?
The difference is that moderate Muslims are much more likely to support Al Qaeda then US Christians are to support the KKK.
For example - from this report from Pew Research:
Where Terrorism Finds Support in the Muslim World - Pew Research Center
One section asked Muslims from 6 predominantly Muslim countries "how much confidence they have in Osama bin Laden to do the right thing in world affairs." The percentage of respondents who said "a lot or some" in each of the 6 countries:
Jordan - 61%
Pakistan - 52%
Indonesia - 36%
Morocco - 26%
Turkey - 6%
Lebanon - 4%
And these numbers were generally down from a couple of years before this poll.
From the same site, they also asked Muslims in those countries "Some people think that suicide bombing and other forms of violence against civilian targets are justified in order to defend Islam from its enemies. Other people believe that, no matter what the reason, this kind of violence is never justified. Do you personally feel that this kind of violence is often justified to defend Islam, sometimes justified, rarely justified, or never justified?" The percentage of respondents who said "often or sometimes" in each of the 6 countries:
Jordan - 57%
Lebanon - 39%
Pakistan - 25%
Indonesia - 15%
Morocco - 13%
Turkey - 14%
These numbers were also generally lower than they were a couple of years earliers.
If you asked US Christians how many have confidence in the leader of the KKK to do the right thing, or how many think suicide bombing or violence against civilian targets is justified, I suspect the numbers would be far lower than the equivalent questions put to Muslims.
Not to say the majority of Muslims aren't peaceful, or do not want peace, but as a population, even Muslim moderates are far more likely than Christian moderates to support violent activity and extremists within their religion.