That article doesn't support your point. The law being referenced here is the Anti-Drug Abuse Act of 1986, signed into law 8 years earlier by Reagan [1]. You are correct, though. The Black Congressional Congress and the majority of black congressmen at the time supported the ADAA, even helping draft it.
But, I still think that it would be wrong to assume that there was universal (or even majority) support among the black community. One confounder would be the media; studies have shown that public opinion about drug use and drug crime were/are directly related to media coverage [2]. With Reagan publicly saying drugs "are as much a threat to the United States as enemy planes and missiles", I think it's difficult to disentangle anyone's true personal feelings about the law from the sociopolitical influences that were present at the time.
The view of policing at the time was simply different. Some might have viewed the ADAA as a much more honest form of policing black communities, as opposed to the efforts undertaken in the 1960s and 1970s: stifling civil rights-related protests and other actions, along with actions by high-powered militarized SWAT teams being concentrated in poor black communities [3].
Even in retrospect, the issues are complex and unclear. Is it really difficult to believe that most people at the time, policymakers or not, were simply incapable of fathoming the results of the ADAA? It's clear that the imbalance in policing, partially as a result of the ADAA, has decimated the black community. Most of the damage, I would argue, is due to an ugly amalgamation of the rise of the prison industrial complex and the transparent willingness of policymakers to look past the needs of poor and minority communities in writing criminal law over the last 30 years.
[1] https://en.wikipedia.org/wiki/Anti-Drug_Abuse_Act_of_1986
[2] https://academic.oup.com/socpro/article/41/3/425/1671880/Set...
[3] https://www.washingtonpost.com/news/wonk/wp/2016/05/02/ameri...