The thing is that any form of Christianity remotely resembling what is found in the New Testament is a lot tougher, more "extreme" if you will, than Islam as such- in two areas in particular I have had a lot trouble in my Spiritual life bringing them under a somewhat at least what is demanded of us condition but these are areas where if I was Muslim I would see far, far, far less in my soul as problematic. A lot of Muslims themselves will admit that Christian ethics are significantly more demanding than Muslim ones but than they will turn around and blame the defection of the West from God in part at least on Christian perfectionism.
I just do not see a general Islamization of the West happening outside of maybe Ulster Protestants turning Muslims en masse.