A typical example of how the erosion of our Christian values has left us without defence against the encroachment of Islam is that of polygamy.
Multiple divorces and remarriages in the West have created a situation which is similar to polygamy with a man or a woman having more than one family. The only difference with Muslim polygamy is that men and women in the Western variant of polygamy are on an equal footing or rather, if there is a discrimination, it is against men.
In these circumstances, Muslim polygamy has been a much more easily accepted practice, with authorities and police in Western countries turning a blind eye to it, than it would have been the case in the past, when people knew what the word 'family' meant, before the time of constant redefinitions of the term to include homosexuals, threesomes, incestuous couples and all the ever-expanding circle of relationships that the concepts of marriage and family must now apply to.
As it is, it's not clear what the ethical basis for the rejection of Muslim polygamy should be, since we have allowed things that have similar consequences for the children, for instance, left in many cases without a clear father figure or even without a father at all, as in the case of single-mother 'families'.
In many ways, there are a lot of similarities between Muhammed and Henry VIII: they both formed religious principles around their physical needs and personal desires.