----"and this 80% number gets bandied about to justify using hormonal contraception/abortificants."-----
People are very intelligent and they can use all sorts of logical game playing, including yours truly, to justify sinful behavior. This is our nature. While biblical truth(and scientific truth to a much lesser extent) can be used to demolish these arguments, the word tells us that the people wielding these arguments really aren't fooling themselves..... they KNOW that they are committing sin. As to degrees of sin.... I know that each and every sin is capable of sending a soul to everlasting punishment..... but human killing...... I imagine the consequences are grave.
That's why I like reading the website maintained by the atheist pro-lifers...(godlessprolifers.com - I think is what it is)
You don't need to bring in religion or discussion of sin to make a good argument.