On total depravity:

I disbelieve that doctrine, partly on the logical ground that if our depravity were total we should not know ourselves to be depraved, and partly because experience shows us much goodness in human nature. Nor am I recommending universal gloom. The emotion of shame has been valued not as an emotion but because of the insight to which it leads. I think that insight should be permanent in each man’s mind: but whether the painful emotions that attend it should also be encouraged, is a technical problem of spiritual direction on which, as a layman, I have little call to speak. My own idea, for what it is worth, is that all sadness which is not either arising from the repentance of a concrete sin and hastening towards concrete amendment or restitution, or else arising from pity and hastening to active assistance, is simply bad; and I think we all sin by needlessly disobeying the apostolic injunction to ‘rejoice’ as much as by anything else.
- C.S. Lewis, The Problem of Pain

I think that Lewis’ comments here on the doctrine of Total Depravity highlight a shortness of thought (even in that excellent intellect of his) when it comes to this doctrine.

Most people, if they have been raised in the church, believe that the Christian view of morality is of morality as synonymous with righteousness, and therefore morals in general are synonymous with the righteousness of God, which is the virtue of in all things seeking to glorify God in a way that simultaneously respects his gracious law. This overlap view is adopted, I think, because in so many ways it happens to match the various sentimentalities that we see not only in ourselves but in others.

But morality and righteousness are entirely different beasts. Only in religion will you find the idea of righteousness. Speaking of the virtue of righteousness in atheism sounds very odd, like a desperate relic of religion. Likewise, Christians ought to recognize that their idea of morality is only one among the multitudes of moral beliefs in the world, each dictated by its god, each rooted solidly in its religion. This is even true of an atheist, who unwittingly makes a god out of the Ego or Reason. Of course I speak loosely of “gods” here; no atheist would call that a god. I am only insinuating that they have many of the same relations to their object of worship – themselves, reason, pleasure – that a theist has to their god, and they follow and love it like a god.

We can also clearly see that one can be a very moral person and yet not be righteous in any way. I have never murdered anybody, I have never had promiscuous sexual relationships - knowingly having aids and infecting all my partners in their ignorance of that fact (just to make it truly vicious); I have never done drugs or stolen cars or killed cute animals. I’m a very moral person to all appearances. But “without faith it is impossible to please God.” And if this is the case, then it means that we can keep the requirement of the law and yet never possess righteousness. Righteousness by its very nature “tracks”, in a sense, the pleasure of God. If we are not therefore pleasing God without faith, we do not possess righteousness either.

Seeing that morality as we use the word is divergent from true righteousness, not one of us should fall into this snare. This snare is what Lewis traps himself in. He says, “I disbelieve that doctrine, partly on the logical ground that if our depravity were total we should not know ourselves to be depraved…” We certainly do see that we are not morally depraved because we can see what is morally right and wrong - morally in its root, I think, referring to social mores, things that help society (Wikipedia: Mores). But if we were depraved in a righteousness sense, we wouldn’t know that we were depraved because we have already ignorantly suppressed the truth to follow our own desires - which may very well be moral - and there is no reason to think that we do not know we are depraved. We suppress the truth in unrighteousness.

Lewis is identifying morality with righteousness here. But the meaning of the doctrine of total depravity is not that we are as immoral as possible, it is that we lack all righteousness, which means we lack faith. So total depravity is not a complete lapse into immorality, it is a complete absence of faith. This is what it means to be totally depraved: that we behave either morally or immorally, but in either case do not have faith, which is the evidence for our hope. Every one of us who is not in Christ is still under the curse of total depravity because they do not have faith. This doesn’t stop them from recognizing “goodness in human nature” as Lewis supposes.  In fact, it leads to us seeing goodness in human nature: particularly ourselves.