You said it’s an out of date concept. Why would something that is rational and reasonably applies to present day be considered “out of date”?

A purely “rehabilitative” justice system would merely be abused by just about every single criminal. There would be zero repercussions.

Many criminals perform a crime because they believe that there won’t be any repercussions. Literally changing the system so there are no repercussions would cause crime rates to explode causing a complete destruction of our society.

I find it humorous how you’ve altered my statement of “the punishment should fit the crime” and molded it towards “children deserve to go to prison with adults”, which is not what I stated.