I think I'm in agreement with you on the terminal/instrumental bit.

The idea of justice as a terminal value...

I don't understand. Do you think justice has terminal value, or just instrumental value?

Punishment may very well be the best way to minimize harm. I'm not saying it necessarily isn't. I'm just saying that hurting a criminal has negative terminal value. As far as I can understand, the terminal value of punishment is what this post is about.