Baptism by immersion isn’t a mormon thing because we believe it’s symbolic of a worldwide flood, it’s a mormon thing because it’s in our scripture: “The person who is called of God and has authority from Jesus Christ to baptize, shall go down into the water with the person who has presented himself or herself for baptism, and shall say, calling him or her by name: Having been commissioned of Jesus Christ, I baptize you in the name of the Father, and of the Son, and of the Holy Ghost. Amen. Then shall he immerse him or her in the water, and come forth again out of the water”
(And for the record, I don’t criticize other churches for holding different beliefs about baptism or doing it differently. Sprinkle all you want.)
I’m sure you’ve encountered the answer before, iepuras. We don’t believe a prophet stops being a fallible man when they become prophet. “Error-free” or “infallible” aren’t words we associate with our mortal church leaders.