You would baptize someone who has already been forgiven for the same reason Paul baptized the Philippian jailer who had already believed on the Lord Jesus Christ. An unsaved person is dead in trespasses and sins cannot obey commands like "Be baptized." "Believe on the Lord Jesus Christ and you will be saved," said the apostles to the jailer. So I agree that water baptism does not lead one to Jesus, as you said. Water baptism is a sign that you have come to Jesus, that you are saved.
The previous poster to which you responded is in error. You aren't forgiven until you're baptized, because until you are baptized, you're still in sin, and sin separates you from God.
Mk16:15-16
15And he said unto them, Go ye into all the world, and preach the gospel to every creature. 16He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
Acts 2:38
38Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
Acts 22:16
16And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.