Acts 10 indeed proves many people incorrect. But it also validates the NEED for baptism, though not in the way many think.
Peter had a vision of unclean animals whom he must "slay and eat". Peter refuses in the vision, and God rebukes him, telling him to not call "unclean" what God cleansed. Peter has no clue what God is trying to say.
So he goes with Cornelius' servants to the house and realizes THEN what the vision meant. GENTILES were considered unclean in the O.T., and God was changing all that and bringing them into the church.
Now, what would SLAY AND EAT represent, if the unclean animals represented gentiles?
Slaying is obviously a connotation of death with Christ. EATING, I think, refers to receiving the GENTILES into the BODY.
Now, God KNEW Peter would hesitate to deal with the gentiles properly. Hence, the need for the vision. Think about it. Would Peter have baptized these gentiles without the vision?
Baptism is sort of like a covenant contract. Two signatures OR SEALS are required on every contract. There is the SEAL of the Holy Ghost and the SEAL of baptism. God's signature and our own. Yes, they would have been Spirit-filled, but somehow BAPTISM is part of putting one into the BODY of the Church.
Peter had to both slay AND EAT.
...Some ramblings of my own.