The state's avowed interest is in making sure welfare money isn't spent on drugs. By testing, they're assuming that the presence of a drug in one's system means one has spent money for the drug in question. While that assumption is probably valid where heavier drugs like heroin, coke, and meth are concerned, it's not necessarily the case for party drugs like pot. Many people who smoke pot never actually buy it. They only smoke at parties or when a friend drops by to share a joint. Sure, some people spend the rent money on bud, but many occasional tokers never spend a penny for it.

Denying someone welfare solely on the basis of THC being in their system, with no evidence that its presence indicates having spent money for it, is hypocritical. Let's call it what it is: using the allocation of welfare funds to enforce morality.