Well, yes, but since many men in other parts of the world have more than one wife, and as a result can have many more children, we should take up those practices as well if we are going to compete in the race to populate the world.
It isn't a matter of competition.
It is a matter of giving up on the future or working toward the future.
If there are 1 billion Muslims going to 1.5B and there are 800M Westerners, going to 1B, say - the West isn't "winning" some battle of sheer numbers.
B ut it is maintaining and growing its population and remaining large enough to defend itself.
If there are 1B Muslims going to 1.5B and there 800M Westerners going to 400M, that's just cultural suicide.
Good point. There's no way a nation of monogamists can keep up with a nation of polygamists (especially if they invade and steal your women too.) /sarcasm