What you say holds true for illegal drugs (once you are in an illegal market, you have limited ways to know what's in what you are taking, and no remedy against

What you say holds true for illegal drugs (once you are in an illegal market, you have limited ways to know what's in what you are taking, and no remedy against the company), but making it legal doesn't change that - you need regulation and oversight. It doesn't get any safer if questionable companies can continue to make low-quality or unsafe products without regulations against them.