A comment from Justin on a recent αλλα post noted:
I ran into a funny αλλα recently. In 1 Peter 3.16 there is a use that seems to develop the previous verse thought. If it were to contradict the previous thought it would be a really strange translation. Check it out and let me know what you think.
Here's the response I emailed back to him:
There's a lot going on in 1Pe 3.13-16 with both δε and αλλα.
One of my contentions/thoughts about αλλα is that yes, it is a marker of contrast, but contrast has a range -- is isn't simply on or off; it is more like a dial than a switch. The range has to do with contextual cues. When the context of αλλα involves a negative then a positive (e.g., "not [that], but [this]") the contrast is high. Contrast is similarly high with positive-negative context (e.g., "[that], but not [this]").
There are, however, a small portion of αλλα that seemingly involve no negative (at least directly). The two αλλα in 1Pe 3.13-16 fit in this group. So I'd say they're still contrasting, it is just not as blatant because the author isn't using contextual cues (positives/negatives) to amp up the contrast. In vv 15-16, the contrast is much more subtle, having to do with the way the defense is made. A more amped-up way of saying it would be, "Be prepared to make a solid defense, but don't bite the guy's head off". The contrast is in the way the defense is made, it isn't made ... er ... defensively, it is made positively and respectfully but strongly. Peter didn't use the amped-up version, and he did that on purpose because that was what he needed to do to make his point. The spotlight is still on the portion following αλλα (make the defense with gentleness and respect); that is the important bit of the comparison/contrast.
At least, that's what I think right now. I hope to look into each of the non-negative instances (there are over 90 of them) a bit further over the next months.
I've got a lot of work to do before finishing this paper ...