There are so many substances out there that are so much worse for the human body than marijuana, and these substances are LEGAL. Tobacco is much worse in the long-run, and it's legal. Alcohol? It's legal. Hallucinogens like salvia? It's legal.
The most marijuana really does is relax you and make you hungry. It's helpful for those who need that extra boost in increasing appetite and helping to gain weight, especially those with eating disorders or those who are going through medical treatments.
By creating a marijuana production industry, we'd also create jobs in the sale of the product as well, decreasing unemployment. It would be a federally recognized job, being paid wages as any other job would as well.