Mary, the mother of Christ, was married age 12 to 15. King David arranged for men to be killed so he could marry their wives. Even given the most parsimonious interpretation of the facts and taking your complaints entirely at face value, Mormonism is no crazier than the Old or New testaments taken at face value.
Which raises the question of why you’re malding about Mormonism in particular so hard. Do you feel a little… inferior perhaps?