The teaching of the Catholic Church on the effects of
original sin addresses both the
free will of fallen man and the capacity of both sinners
and non believers
to do good.
The fact that fallen man--after the
sin of Adam--possess free will is demonstrated from the Bible
John 8: 33-36
They answered him, "We are descendants of Abraham
and have never been enslaved to
anyone. How can you say, 'You will become free'?“
Jesus answered them, "Amen, amen, I say to you, everyone who commits sin is a slave of sin. A slave does not remain in a household forever, but a son always remains. So if
a son frees you, then you will truly be free.