How exactly is smoking tobacco more dangerous than smoking marijuana? They both have lung cancer risks and expose others to second-hand smoke and the dangers associated with that. Cigarette smoke however is not going to make the user or others exposed to the smoke impaired, or in any way affect their ability to work/ perform tasks that require mental clarity and a quick reaction time. Marijuana use has neurological and cognitive effects that tobacco does not have. Numerous studies have shown the link between regular marijuana use and memory loss, decrease in IQ and cognitive thinking, as well as significant alterations in actual brain structure. I find it interesting that there's such a huge campaign against cigarette smoking, while smoking marijuana recreationally is being advocated for.
Comparing alcohol and marijuana is a difficult issue. They are two completely different kinds of substances. They both certainly have potential for abuse and can affect one's mental clarity and slow down their reflexes. I can't argue that for many people, alcohol use will make them far more violent than if they were to use marijuana. Someone having a drink, however, does not affect the mental clarity of those around them or place them at second-hand smoke exposure risks.
Alcohol can also be easily, quickly, and accurately tested by police and employers to decrease the risk of drivers and employees from exposing others to danger while driving or working impaired. While research is being done to find an equivalent test for marijuana, right now the saliva tests are not completely accurate, have potential for manipulation, and also have a higher than what should be acceptable false positive rate. We don't have a widely accepted standard for what classifies being intoxicated and it is difficult, if not impossible, to ascertain based solely on the amount of marijuana in a person's body that the person is currently intoxicated, smoked yesterday, or was merely exposed to second-hand smoke. This is personally the biggest reason I am opposed to legalization. We need to do more research to create a standard for what constitutes intoxication and a way to quickly and accurately measure that, and we just aren't there yet. Many studies have shown that people who test far lower than the 5 ng/mL acceptable amount in certain states perform in mental and physical testing in a manner comparative to someone intoxicated. The roadside THC device currently being tested in MI only detects 25 ng/mL or higher according to the manufacturer.
Several studies indicate a clear link between marijuana use and schizophrenia and show that the risks are greater the younger someone starts using. Few teens and young adults seem to be aware of these potential risks.