I agree with your statement, legalizing marijuana will reduce the numbers of people in jail making room for people who have actually committed a crime.
Marijuana should not be legal because it impairs your attention ability. It will cause students to get misguided in their schoolwork resulting in low grades/carelessness.
Even if marijuana doesn't get legalized, people will still find a way to use. Marijuana is still going to cause millions of deaths even if it's not legalized.
There are multiple long term effects reduced;volume of specific brain regions involved in a broad range of executive functions such as memory, learning, and impulse control.
Legalizing marijuana will increase the income. Which means more money to your communities that can be used for fixing the streets. building parks, and maintaining a clean environment.