I think the problem in the US is the odd way you prosecute - you can do 'one thing' and up getting charted with '10 things' and getting 10 stacked sentences which adds up to 100 years.

Also - the punishment for small amounts of weed in most states is insane.

Likewise - the drinking age is crazy high in the US.

Some minor changes in the law could really quite radically affect how many people are in jail.