Justification before decision still works out better in practice, though, because of chain of thought [1]. You'll tend to get more accurate and better-justified decisions.

With decision before justification, you tend to have a greater risk of the output being a wrong decision followed by convincing BS justifying it.

(edit: Another way you could think of it is, LLMs still can't violate causality. Attention heads' ability to look in both directions with respect to a particular token's position in the sequence does not enable them to see into the future and observe tokens that don't exist yet.)

1: https://arxiv.org/abs/2201.11903