While science is in theory "perfect", unfortunately the people doing the science are still just flawed, imperfect humans. Even scientists who have no malicious intent can still have their work influenced by unconscious biases if they aren't careful.

Given that, I think "consensus" is a useful term. It suggests that a strong supermajority of scientists have findings that agree with something, and with that chorus of agreement, it's harder to oppose those claims by accusing all of those scientists to have flawed results.

I think you can probably find a lot of science out there that supports criminalization of drugs, and showing that there's a "growing scientific consensus" on the failures of criminalization is useful to show that previous research on the subject has either been debunked or proved false by later observations. Because that's literally what's happening.