It's simply that our reason isn't "Lord."
Actually the author of this thread's article brings this out well...when he closes the article with this comment:
So in a sense, the teaching of infant baptism reveals who your Lord is. Lord Jesus Christ has commanded us to baptize all nations, has declared that everyone who dies without faith is damned, and has taught us that infants can believe by God's grace working through baptism. Lord Reason says, "I don't understand how a baby can believe, therefore I reject infant baptism. It makes more sense to me to do it my way." Which Lord will you obey? Will you obey Christ and baptize "all nations," including infants, even though you don't understand it? Or will you obey Reason and reject infant baptism because you don't understand how babies can believe? Which Lord will you obey?
If infant baptism is the imperative that the article states, why did God not set that example at Jesus’ birth? God could have certainly set the timing of John The Baptist’s arrival to coincide with the Jesus’ birth. It was the event of His baptism at age 30 that ushered in His ministry. I tend to believe that Jesus, sinless and in no need of salvation or baptism, set the example and significance of baptism as the conscious act of a disciple in obedience to God’s command. An infant cannot make such a choice.