Featured All Humanity Originally In The Book of Life?

You bring up a good point.
First, if all are in the book (fully perfect, without sin) then the teaching would be full blown Pelagianism. (10 Things You Should Know about Pelagius and Pelagianism)
Second, which sin would be the action that would cause God to erase someone from the book?
Third, what human action would get someone back in to the book? (Some here would argue that you must repent and be baptized to get reinstated).
Fourth, what actions, after repentance could get you erased again?
Fifth, when would the cycle of repentance end and could one accidentally be in a moment of unrepentance that thus sends one to hell?
Finally, where has grace gone?

 

In another thread, a person asked an interesting question.
Why stop abortions?

Grant it that I believe God extends grace to the aborted child, both those God gives over to death in the womb and those taken by the evil actions of men, but the question still remains...if all humans are born righteous, without stain of sin and only can lose their standing by having God blot them out.

Such an idea seems completely contrary to God's revealed word, yet one person, at least, believes it to be true.