As far as the policies of when and where to test, whether the evictions were punitive (ie against users) or based on the prevailing perception of safety - I don't know.
Under the tenancy agreement I signed as a Tenant. If I have/use illegal drugs on the premises, I can be be kicked out and then have to pay costs associated with clean up. Property was tested (clear) before I moved in.
That all seems fair enough to me as tenant.