Bob gets caught smoking some pot, and has two kilos in it in his room. He goes to prison for several years. There he is raped and brutalized, and when he is released, he's lost any sense of empathy or respect for law and order. He kills and rapes a woman in an alley, but is subsequently caught, and is sent to prison for the rest of his natural life. There he brutalizes the "newbies" and the cycle continues.
This benefits society, how? "Bob" is fictitious, but stories like this are real. Our goal should be the overall good of society, not instinctive "he should have thought about that before he committed a rime!" responses.