It has nothing to do with suspicion...... the point is not "being on welfare makes me think youre a drug user"....
employed people.... tax payers.... the people who pay for welfare..... have to take a drug test as a condition of employment. I could be drug tested today...... i can refuse to take the drug test if i want. Welfare recipients are required to be actively seeking employment as a condition of being on welfare. They should be required to take a drug test as a condition of receiving that aid. Something they can chose not to do if they want. You will decide to either volunteer to take a drug test or not volunteer to take a drug test. If you're not willing to volunteer to take a drug test, then you're not willing to accept employment, because that is the first thing an employer is going to ask you to do.
If we're arguing the technical details of it....... i'm OK with welfare recipients not being drug tested..... just enforce that they seek employment and set up a program for employers to report anyone denying a job offer or failing a drug test. If you reject a job or fail a drug test..... best of luck to you, no government check.