6. Baptism must be include an understanding and acceptance of the faith. Catholics baptize at birth, then allow the children to understand through catechism (I would know, I went through most of it). If we take notice of Mark 16:16, we read "He that believeth and is baptized shall be saved; but he that believeth not shall be damned." Never does it state it in the reverse.Indeed. But look at the audience: they are adults. Of course adults have to believe. It is this belief that compels them to be baptized. Now, infants can't very well believe first, but that doesn't mean they shouldn't be baptized. We are all born with original sin, are we not? Paul says, “We are all by nature children of wrath” (Eph 2:3). This sin separates us from Him. Thus, it would be a great disservice to deprive infants of the source of grace that they so desperately need. Jesus said, “Let the children come to me, and do not hinder them; for to such belongs the kingdom of God” (Lk 18:16). The kingdom is just as much for infants as it is for adults, and baptism is how they gain entrance to it (cf. Mk 16:16; Jn 3:3,5; Acts 2:38; 22:16; Rom 6:3-4; 1 Cor 6:11; Titus 3:5; 1 Pet 3:18-21).
Also, faith is not actually absent from the equation because, in infant baptism, the faith of the Church community stands in for the faith of the child. This may sound peculiar at first, but there are in fact many examples in Scripture of someone receiving grace and healing because of the faith of someone else. For example, the centurion's servant was healed because of the faith of the centurion (Mt 8:5-13). When the paralytic was lowered down through the roof to be healed by Jesus, He healed the man and even forgave his sins because of the faith of the paralytic’s friends (Mk 2:3-5). Jesus rescued the soul of a child because of his father's faith (Mk 9:22-25). Finally, Paul says that children are made holy by the joint belief of husband and wife (1 Cor 7:14). All of these examples are analogous to what takes place in infant baptism, when a child is cleansed of original sin because of the faith of the Church.
There is also a lesson to be learned from the relationship between baptism and circumcision. In the Old Testament, Jews circumcised their children when they were 8 days old, and in so doing, made them members of the covenant (Gen 17:11-12). They became heirs to the promise and Abraham's offspring through circumcision. Now, we become the same through baptism (Gal 3:26-29). Baptism is the new circumcision (Col 2:11-12). And so, in similar fashion, we baptize children so that they may gain entrance into the new covenant and become children of Abraham.
Finally, we know from historical documents that the early Church baptized infants, and there are indications of this in the Bible as well. In order to emphasize the universality of the sacrament, Peter says that the gift of the Spirit received in baptism is a promise not only to them, but to their children, and to all that are far off (Acts 2:38-39). This wide scope of baptism also explains why entire households were baptized (Acts 10:47-48; 16:15,30-33). Note that the Greek word for “household” is oikos, which means “the inmates of a house, all the persons forming one family, a household” or “stock, family, descendants of one.” There is no reason to believe that the children in the house were not baptized along with everyone else.
Thus, the stain of original sin, the right that infants have to the kingdom, the role of the Church’s faith in the lives of Her weaker members, the parallel between circumcision and baptism, and the universality of the sacrament all demand that baptism be given to infants as well as adults.
Now, on to your next point ...