Once again a Muslim extremist group is damaging Islam's brand

But Islam has always grown via violence and coercion rather than persuasion. The Muslims conquer a country and then slowly socially and economically strangle  non Muslims into converting.

A great strategy if you are a dominant economic and military power but Islam is anything but that. Any place where Islam isn't dominant it is likely to repel rather than attract converts. In those environments Christianity's sophisticated, modern message beats Islam's brutal midievalism every time.