Making fashionable designer goods is legal. That doesn't stop anyone from creating fake stuff and selling at cheaper cost. Everything like alcohol, shoes, purses, clothes, paintings, etc gets sold in black market. So that establishes the fact that there will always be black market even on legal stuff. Which means that legalization is not going to curb criminals.
Now about revenue. Surely it will bring it tax dollars. But is that the business government want to be? Collecting money from people's drug addiction? Is it morally right for a society to benefit from someone's addiction? That's a question where everyone will have different answer.
I do support legalization of Marijuana if it benefits medically. Let that be controlled. And not highly taxed. If it's classified as medicine, it should be affordable.