Someone who smokes pot all day will obviously be impaired and unmotivated. Just like someone who drinks or takes pills all day. The difference with pot is that it is non-toxic and only mentally addictive so an addict who resolves the mental addiction will not have permenent damage. It can also be grown almost for free so there is no need to steal.
What about the people who can't work due to addictions to booze, video games, porn, facebook, etc?
Should we ban everything that is potentially addictive to a few percent of the population?
There are countless cases of people who OD on drugs because of one bad trip. This rarely happens with alcohol.
Pot is largely a young person's drug. It opens the world of drugs to young minds.