There will be an increase of tourism here in the US since it isn't legal in most countries. Thus bringing even more money into the economy.

If it becomes legal there will be more scientific research about it.

Many people who buy Marijuana usually buy it laced or mixed with other drugs. At points the consumer may think they are consuming Marijuana but in reality it isn't. With the legalization of it the FDA will most likely check the drug before it selling it to the consumer thus preventing the mixture of other drugs.

If it became legal then people who are addicted to it will be more open about it and about getting help. They won't get judged as much since everyone will be able to use the drug.

If it became legal it still would not be "legal" everywhere. For example people would most likely not be able to have it in schools or while traveling with it on planes. They would still be more prone to getting arrested.

It will be better for the environment since it will most likely be in large demand. People will start growing it and cultivating it.

If this drug becomes legal it will reduce drug trafficking since it will be more available here in the US.

Studies show that constantly using Marijuana causes infertility.

It can cause problems when driving. Since smoking it will "become normal" people will most likely be high when driving causing accidents.

If Marijuana become legal then it will open the door for more drugs to become legal as well. For example the people will start asking for other drugs to become legal as well and if not it will be seen as unfair.