In the case where someone wishes to commit a crime so they can spend time in jail, they'll probably perform something petty, which isn't TOO bad especially if they can confess and the goods be returned (or an equivalent). If social planning can lower the poverty rate and provide ample social nets and re-education for people in a bad spot in their lives in the first place, this thing is also less likely to be a problem (conversely, if more people become poor, prisons will be pressured to become worse to keep them below the perceived bottom line). Finally, prison can be made to be nice, but it isolates you from friends, family and all places outside the prison, and imposes routine on you, so if you desire control over your life you'll be discouraged from going there.