Herve, you should be scared, very scared.
From: http://www.religioustolerance.org/isl_numb.htm
As of mid 2010, we accept the Pew Forum's estimate 1.57 billion as the most reliable estimate.
With that number, they represent about 22% of the world's population. They are the second largest religion in the world. Only Christianity is larger, with 33% of the world's inhabitants -- a little over 2 billion.
Islam is growing about 2.9% per year. This is faster than the total world population which increases about 2.3% annually. It is thus attracting a progressively larger percentage of the world's population.
Please refer to the last column in the chart:
http://www.religioustolerance.org/worldrel.htm
Word of caution Herve: the next time you check into a motel (I believe a hotel is beyond your budget 😂 ) check the dresser drawers - you might find a Koran sitting beside a Bible.
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The Christian population in western countries has been on the decline. It's not to say that Christians converted to another religion, but the majority are more likely lapsed practitioners. This decrease in population was brought on by no other than the Catholic Church itself.
There is a growing population of people from all religions who, for one reason or another, stopped "practicing" their religion. These people more than likely have limited their belief to believing in God, living on the the basic knowledge as to knowing good from bad/right from wrong, and go through life based on reality, rather than what is dictated by a religion.