part 1
Islam is the fastest growing religious group in the world these days. Even though the number of people converting to Islam is growing at a strong rate, the main reason for this should probably not be sought in convertites but be attributed to the fact that all major schools of islamic law are against abortion if the life of the mother is not in danger, thus contributing to very high fertility rates in dominantly muslim populations which in turn is lending to a strong growth of these population segments. Similiar issues apply to other forms of birth control.
Christian societies, on the other hand, tend to have rather low reproduction rates in these modern times (AFAIK, the USA are the only christian country in the West with an average fertility rate of >2). This can be attributed to the christian churches not having the firm grasp on society and its laws they had in medieval times and the simple fact that the one strongly growing population segment of christian-dominated societies (i.e. "the west") has realised that limiting the numbers of offspring to support automatically rises the ammount of benefits they are able to spend on themselves, thus having eroded the traditional proletariat of the working class era. The simple lesson "Don't reproduce excessively if you are on the lower end of the social strata" finally catched on and the material considerations based on this, equally applicable in both more capitalistic and more socialistic countries, have overruled the moral considerations of the religious dogmas.
This is not true for the dominantly islamic populations. Voluntary infertility here is not only going to piss off your imam and the rest of your muslim community, it also will not significantly improve your chances of rising on the social ladder. Muslims are mostly trapped in the respective demoninational rackets they happened to stumble into by birth. Either they are shunned by the middle class in christian countries as everything from suspicious foreigners to lowlife immigrant scum, or there simply is no middle class to join (as holds true for most islamic countries). Within these rackets, cheap human capital is the only social currency they can offer their upper ranks. Big ammounts of cash flows into the direction of those families who can afford to sacrifice one of their sons because they have two to four others who themselves are without any chance to find a social position in form of a high-ranking office or a substantial heritage. Gaza Strip, for instance, has a total fertility rate of 5.64, while Israel has to supply its army with only 2.38.
end of part 1
part 2
Another major factor are the relatively high mortality rates within islamic societies which are the reason for the age structure of these populations often forming a youth bulge, i.e. very high percentages of young people who make up for a very aggressive competition force within that very population, often leading very many of these young people taking very extreme measures to get their fair share of material success - in opposition to balanced age structures in which enough old people exist who usually got old by holding on to what they have already acquired and whose main prerogative is to protect that gain by keeping society in harmony. Again, the impossibility of a dominant ammount of a muslim population in a society joining the middle class or even making up that middle class itself, sustains this population profile in most islamic countries.
Without any doubt, religious dogmas and their tenets of inherent or culturally related ideologies have their fair share of keeping the wheels of their respective societies in motion. Yet, it is unwise to see in them the actual cause of what their societies continue to sow and harvest. All major religions have sacred texts or textual passages which can and have been used to justify any imaginable sort of crime. But the cause for these justifications rarely being called upon today in all but Islam is not to be looked for in the justification themselves, for these justifications are dominantly only something that instated post facto, to justify a crime that has already been committed or decided on. After realizing this, appeal to individuals to refrain from committing these crimes is begging the question on what motivated their crime in the first place. But the individual rarely has a choice within a racket. They got nothing to lose and what little they can gain they can only gain through extreme measures. Islam, as an ideology supporting crimes will only transform into something as tranquil and peaceful as most christian churches when the societies which are the religions' soil transform in the same way as the christian dominated societies have. Without the creation of a dominating middle class in these societies the power supplies for the rackets that need to pacify the minds of their members who live with the crimes they committed with the opiate of religion will never be cut off and the day of Islam's transformation will never come.
end of part 2
Don't worry. They'll get over it.