By a large margin and it's not even close.
1)It's most likely the leading cause in the rising anxiety epidemic among children with a massive impact on female children. Rates of suicide, attempted suicide, and self mutilation have skyrocketed amongst female teens since 2010.
2) it's being weaponized by authoritarian and communist regimes like Russia and China to cause unrest and civil crisis in democratically elected countries and it's been devastatingly effective. Without social media there is no trump presidency, no brexit, and nowhere near the massive populist uprising in countries all over Europe, South America, and Asia that we're seeing today.
3) it allows people who are giant pussies and would never say anything negative, mean, or vile to someone face to face to act like giant pieces of shit because the threat of physical violence and death is removed. It's caused a massive blow to civility and civilized conduct.
Zuckerberg and Jack have unleashed a horrible plague upon humanity that the likes of Hitler could only dream about.