The dialog becomes impossible because of many other important reasons, too, including,
a. the opposition by liberals/leftists/Islamists to bring forward any critical review of some extremely troubling vicious aspects of Islam and Islamic scriptures (Quran and Hadiths) under the phony reasons of islamophobia
b. the reluctance of Islamists to accept the notion of freedom of expression even if it means some of the expression offends the Muslims (e.g. discussion regarding pedophilia of Muhammad or someone drawing cartoons of Muhammad)
These views by Bill Maher and Sam Harris may help understand this point in a better way. [1], [2], [3]
In fact, the freedom of opinion is under attack because of Islam, even in the free western world to a large extent.
The freedom lovers, liberals and humanists must understand this threat posed by the vicious ideology of mainstream Islam. The USA and the west now must also invest similar (if not more) efforts and resources to fight this vicious ideology as those that they invested to fight another vicious ideology called communism.
It should however be noted that there are many people who have been Muslims just by birth and they do not necessarily follow the vicious ideology to its core.
So the fight must be against Islam and not against all Muslims, per se.
[1] https://www.youtube.com/watch?v=8E1u9lQeAsY