Baptism is a sign and seal of regeneration. Regeneration is a saving act of God wherein man is totally passive. God removes the heart of stone and gives him a heart of flesh. Man cannot regenerate himself nor participate in his own regeneration. Baptism is an outward sign of regeneration. That is its meaning...............
I don't believe that baptism is primarily a sign and seal of regeneration as you say it is although the fact that one has been regenerated may well be a part of what is signified by baptism.
Baptism signifies one's death to the old world you were originally born into and the rebirth into the Kingdom of God.
That birth into the Kingdom finally comes about through the hearing and acceptance of the Word of God.
"... you have been born again not of seed which is perishable but imperishable, that is, through the living and enduring word of God." 1 Peter 1:23
It does not come about through regeneration - even though (apparently from the scriptures) one must be so regenerated by God's Spirit before he or she can be born again by understanding the gospel preached to them and responding to that Word.
Your life in this world was not generated through your birth. Your birth was the inevitable result of your having been generated beforehand. That was an act shrouded in secrecy and mystery. Likewise is your spiritual "regeneration".
Your birth, on the other hand - was a time of rejoicing for everyone concerned.
Likewise should it be with your spiritual birth. It's should appropriately be open and laid bare for the world to see.
"for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation." Romans 10:10
It is the same with the rebirth by being "born again" as the Lord puts it as it was for your original birth. There is a reason why He chose that metaphor.
Baptism is primarily a picture of the rebirth process – not of regeneration.
It symbolizes repentance (or death to the things of the old world) - our lives being hidden in Christ through His death – identification with the resurrection of Jesus Christ showing His sacrifice being acceptable to God – and our coming forth into a new world as a completely blood washed child of God - never again to die in our spirit.
I suppose that there is nothing inherently wrong with infant baptism - since apparently whole families were baptized in the N.T. record (such as the case of the Philippian jailer and his family).
But such infant baptism cannot adequately show forth the time when one is born again by the living and abiding Word of God. For that to be the case - there must have been personal time when the person believed the Word, died to the old world, and began a new life in the Kingdom of God.
Thus - IMO - re-baptism is not only appropriately allowed. It is desirable in the life of every truly born again Christian.
I suppose the Lord will have to sort us all out when He comes again for judgment.
But it has been my experience that - having been an active elder for many years in the lukewarm (to be charitable) Presbyterian Church and having taken a strong stand against the errors of the Catholic church for most of my life - many of those baptized as infants in the so called church never do come to the point of being born again.
But that's probably a subject for another thread.