From a logical POV, (presuming, of course, that God is omnipotent first cause, and presuming any logical implications of that fact), there is abundant reason to agree with the Westminster there, and with Scripture's statements to the subject of Total Inability. Logically, that is, man has no ability in and of himself, to any good, apart from God "in whom we live and move and have our being". It is altogether reasonable to assume that though mankind is made in the image of God, that it makes no implication that he is in and of himself good, nor independent, in the way God is. (The only way that even freewill of the usual use is implied is by the assumption that freewill is the only way for a man to be morally responsible for his actions (which, as has been shown elsewhere, is self-contradictory, considering the very meaning they intend by "freewill"). )
But that he is in Adam identified with enmity against God, by both inherited effect and by imputation, and which fact is affirmed by his own continual practice, places him wholly against God, corrupt to the core, no matter what good deeds he is credited with by his own conscience or by the assessments of others. This is an enormous step beyond mere innocence, such as instinctive beasts have, or even such as Adam had before his disobedience.
Fallen man is not just morally bent --he is broken, no longer capable of moral good.