Yes, pot should become illegal and, in fact, is illegal under federal law. Despite states voting to legalize recreational marijuana, possession remains a federal offense. Psychologically addicting, marijuana use also causes adverse physical and emotional effects, including increased anxiety and depression. Safety on the roads is a major concern as driving under the influence is prevalent in the U.S.
Many states have already legalized pot for medical or recreational purposes. We need to have a uniform national policy for marijuana use and for the growers. Pot is going to continue to be a drug that citizens use and grow so it is better to made it legal and be consistent across the nation.
If it really is harmful, something I don't think to be true, people should still be allowed to do it. It's taking away the choice that really makes it messed up for it to be illegal. Many people will also say that people driving under it's influence can crash and die. *cough ALCOHOL *cough.
The war on drugs has clearly failed us, as we have people serving time and entering the prison system for small amounts of marijuana. The states that have already decriminalized marijuana and choose to sell recreational cannabis are earning a huge profit, and supplying a safe transaction for people to purchase what they were already purchasing. By making pot legal, the state benefits from the taxes, and the people get a safe product at a reasonable price, from a safe store front.
Regardless of personal preferences, it is becoming less and less deniable based on scientific research that alcohol is actually more damaging to the human body than marijuana. Indeed, most agree that there are more positive effects than negative side-effects. The most convincing argument, that marijuana serves as a "gateway drug", has become less and less convincing based on market research.