Drug Testing for Welfare Recipients

Due to the fact that welfare and other public benefits recipients are no more likely to be drug users than the population at large, why are a number of states considering imposing drug tests to those beneficiaries?

Some other questions come to mind:

What are the unintended consequences of such a law? What happens to people when they lose the safety net when they already are struggling with substance abuse issues. 

What is the evidence of welfare benefits being squandered on drug use? How serious of a problem is it? 

Why is drug use the target and not other social harms such as gambling, distracted driving, alcohol use, or smoking?

Isn't drug use already proscribed for welfare recipients? For example, if you are convicted of a drug related crime you may lose your benefits. 

What is the actual projected cost-benefit-analysis of the implementation of these laws?

If anyone out there really thinks that cutting benefits for low-income people is a good policy idea, and not just a way to make political points with voters, I would like to hear why.

More reading: http://www.thefix.com/content/gop-goes-crazy-drug-testing