Some members of NAMI favor the law because it would make their own lives easier. they have people in their families who they consider to be mentally ill. The law would grant them the capacity to coerce their family members into accepting a "treatment" regime of brain damaging sedatives. These people operate under the assumption that such sedatives do not cause more harm than help. They also believe that the people who admister such harsh drugs operate on a scientific grounding.
The industrial financiers of NAMI have an obvious economic interest in the law. They also have an interest in deceiving the public about the true nature of their products. The more that people learn about the deleterious effects of their "treatment" regimes, the less demand there is for their wares.
One of the greatest ironies of Laura's Law is that it was implemented in Orange County, California using the brutal slaying of a homeless man by police as a rationale. I suppose the logic goes that had the man been subdued by brain crippling sedatives, he never would have had a tussle with the fuzz. Proponents of Laura's Law see the need to deny rights to the "mentally ill" before they are murdered by "law" enforcers. There is something entirely unhealthy about this state of affairs.