Note that blindness to sin is a major concomitant of sin. Apart from grace sinners cannot be aware of their predicament. Blind as we are to our sin, our sin can only lead to more sin. We are held captive by sin to sin. Note the peculiar nature of Christian freedom.
Freedom is freedom from sin's captivity and freedom for obedience alone .
As fallen we cannot will faith in ourselves. Bl. is correct to suspect Niebuhr's greater reliance on uneasy conscience than on the HS to convict. This presupposes that, thanks to our uneasy conscience, we can precipitate ourselves towards faith. This suggests we ought to magnify the uneasy conscience.