The primary function of hormonal birth control is to prevent ovulation, yes. But it doesn't ALWAYS do so. There is more than one form of birth control that, as a back-up function, prohibits implantation of an already fertilized egg.
We all know birth control isn't 100% effective. There ARE times when eggs are released, thus potentially being fertilized. Otherwise we'd never have any babies concieved with mothers on the pill - but we do. What we DON'T know is how often that fertilized egg isn't able to implant because of the back up action of the pill (or other contraceptives).
When you read the manufacturer's information it clearly says that as a back up means of birth control it will prevent the implantation of a fertilized egg.
From there it boils down to your personal and/or religious beliefs. IF you believe that life begins at the moment of conception, than purposefully doing something to your body to prevent that life from being nurtured may be unacceptable to you.
