One thing I appreciate is being reminded to interpret scripture by using scripture, particularly the verses before and after!
Why do Lutherans baptize infants when the Bible says, "Believe and be baptized?" This passage teaches that baptism is for the person who has accepted Christ and wants the Holy Spirit to come into his life.
What the passage actually teaches:
Believing in Jesus, that is, having saving faith, is indeed a requirement to receive divine blessings of personal forgiveness through baptism as well as through the Lord's Supper or the Word of God itself. But this is not a prerequisite for baptism. In fact, saving faith is given through baptism.
The Mark 16:16 passage is explained by the prior verse, Mark 16:15. Jesus is instructing his followers to preach the gospel. Then what follows makes perfect sense: whoever believes and is baptized will be saved.
If someone is converted by the Holy Spirit through the Word (as an adult, for example), the faith comes first and baptism will follow (so that the Holy Spirit will strengthen that faith). For obvious reasons, in the case of infants baptism is applied to them to create faith and then instruction in the Word follows to strengthen that faith. Questions or statements based on a person "accepting" Christ and "proclaiming his faith" through baptism are based on a false understanding of how people become believers and what baptism is and does. No one "accepts" Jesus on his own since by nature fallen mankind has no free will whatsoever in spiritual matters. Faith is a gift of God through Word and sacraments. And baptism is a work of God through which God proclaims promises and gives spiritual blessing; it is not given as a human work or testimony or act of obedience.