Weed isn't harmless to everyone. In a subset of people, marijuana has been proven to trigger Schizophrenia in both people with a family history and without. Don't bother saying it doesn't. Scientists have observed it as fact.
My younger brother is a huge weed lover to this day and was diagnosed with Schizophrenia at age 20. Nobody can say for sure the pot triggered it in him but it may have. All I know is, his life is completely ruined. He's paranoid, delusional and unable to function like a normal person. It's heartbreaking to see.
I'd caution anyone with a family history of Schizophrenia to avoid pot. It's not worth the risk, even if most people can smoke it with minimal or no issues.
Like virtually everything in life, weed is not all good or all bad.