cleanmachine
My two cents' worth.
First, partly it's due to simple demographics. Muslim populations have higher fertility rates.
Second, it's due to an association between Christianity and colonialism. Islam is seen as anti-colonial.
Thirdly, Christianity has been massively rejected in its heartland. Islam hasn't. I will not suggest that Christians receive more discrimination than Muslims. However, Muslims do have an advantage in that Islam as a recent import, doesn't have the same background.
Finallyy, it is as a replacement for traditional Christianity. I am a 40 year old traditional hymn-singing Anglican. And there is hardly anybody else my age left, even less amongst younger people. The traditional churches - the Anglicans, Methodists, Presbyterians, Lutherans are all dead in the water except in North America and excepting the dead cat bounce in eastern Europe. They are custodians of ancient monuments who lost their role as custodian of the nation's morals half a century ago.
On Sundays, when I listen to the choir singing Byrd and Tallis, I think that my generation will probably be the last one to hear this stuff sung live and for free.
Christianity like mine has been very partially replaced by a debased sort that doesn't require its leaders to study New Testament Greek, Old Testament Hebrew, classical Biblical scholarship or systematic theology to anything like the level traditionally required and (until recent years at least) placed sole emphasis on evangelism and none on charitable work. The intellectual basis of Christianity is being hollowed out year on year. Subjects like theology, philosophy of religion, church history and Biblical studies have largely been replaced in the universities by sociological alternatives like religious studies.
By contrast, Muslims (as far as I can see) still preach what they've always preached, their style of worship is the same, and in Islam's heartland, one can study Islam (as opposed to a sociological study of Islam) in their universities. When I compare what Muslims do in the mosque with what modern Christians do in church, I have to say that I relate to the Muslims more.
And there is this:
Uh fuck religion and all the shit it causes.
which makes me think, given the hatred, if one's going to practice a religion, it might as well be Islam, which doesn't try to be conciliatory.
And if I were a Muslim, I don't think the existence of ISIS or jihadists would make me doubt my religion. It is easy to distinguish the average atheist's morals from Stalin just as it is easy to distinguish the average Christian's morals from Savonarola, if you make half an effort and employ half a brain cell. Belief (or no-belief) in God doesn't imply anything - it is how you interpret it that counts.