Did people claiming to be Christians murder or collude in the murder of 6 million Jews?
Two can play this game.
How many Christians were among the American jailers at Abu Graib? Let's condemn Chrisitanity for their behavior too.
Chrisianity, by its own measure, is to be reflected in everything that its adherents do, say and think. Therefore, if people who commit evil acts claim to be Christians, and are not immediately expelled by their congregations and their faith, the Christian religion must also be to blame.
This is the test you propose for Islam. Let's apply it uniformly, to see how reasonable it is.
Condemn a whole religion espoused by millions of people because of the acts of a few fanatics at your peril.