Simple: killing 'em when you can't see 'em makes it a lot easier. If you wait till they are born, you also enter into the realm of infanticide.
Remember, a magic process occurs when a baby is born, it ceases to be tissue and becomes a being with its own rights. Best to snuff them out before that occurs.
Anyway, "too many humans on the planet" is only a good justification for suicide, genocide, and homocide. The easiest and quickest option is the first.
Need pro abortion arguments
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