St. Augustine argued somewhat like thus:
- Everything that exists is sustained by God.
- God sustains only good.
- Thus everything that exists is good insofar as it exists.
- Thus evil is only a privation of good.
For instance, why couldn't some evils instead of being privations be mismatches? The mismatch between Jones' belief that Americans never landed on the moon and the fact of the moon landing could be an evil. An ontology could, for instance, include both Jones' belief and the moon landing, but not include as a further item the mismatch between the two. One might try to argue that a mismatch is a privation of a due match. But the correct ontology might not include matches either. Or consider the example, discussed in the secondary literature, of the man with two noses. It's an evil to have two noses, but at least prima facie (sorry!) the extra nose isn't a privation. But if we do not suppose that evil has to be a privation, then we can say that the problem is the mismatch between the face and the human form.
This approach would allow one to retain the central anti-Manichean insight that Augustine has, namely (3), while at the same time escaping some counterexamples. I am not sure it escapes the biggest counterexample, namely pain. Though if we take Mark Murphy's theory that what is bad is not pain itself, but the disharmony between reality and desire that tends to correlate with pain, then the above approach helps, since a disharmony is a kind of mismatch.
I am not claiming every mismatch is an evil. The argument doesn't establish that every "thing" that doesn't exist is an evil (remember the remark that matches might not be in the correct ontology).
Final note: An alternative to the above would be to weaken (1) to the claim that everything that fundamentally exists is sustained by God, and hence everything that fundamentally exists is good insofar as it does so.