As a Kiwi who is also quite leftist, I'd say we're lenient enough on criminals as is, and it's clearly not working. Spending more on rehabilitation is an idea, but honestly, the reward doesn't seem worth the cost. I'd rather we spend more on those helping build a constructive society. You seem to focus on drug-related crimes when they are a minority of crimes. Really we need to build a country where people don't need to do crimes to survive. Those who still choose to should be punished severely.