The doctrine that infants do not need to be baptized is a distinctive doctrine in LDS scripture. There is also a discussion in 2 Ne 31 about the need that Christ had to be baptized. Coming up with a good reason why both of these statements are true seems to be a somewhat difficult theological task.
- see pp. 127-28, 134, 138, 203 and 222 in Exploring Mormon Thought: The Problems of Theism and the Love of God.
Ostler is not as clear as I would've expected on this issue. Basically, he seems to argue that if baptism were a strict requirement, then God would be a respecter of persons (a la Moro 8:10-12; p. 203).
I don't want to implicate Ostler with my view, so I will call this "my view." I'm planning to rework this soon, but here's my view (based mostly on a post I sent to the LDS-PHIL listserv):
Our divine nature and penchant for sin
One might take passages about the natural man to imply that we are born as enemies to God and therefore need to be baptized at birth. However, this does not necessarily follow. Instead, Paul is only saying that we are born with a proclivity to sin (e.g. physical desires).
We can therefore say that we are born with both a divine nature (spiritual potential to be good, and the freedom to choose such b/c of the atonement) and a "natural" (e.g. physical) proclivity to sin.
Accountability and sin
B/c of our own spiritual inexperience at exercising our atonement-given freedom to choose, it is inevitable that we will all sin when we are enticed to do evil. However, to sin, we need to be (old enough to be) accountable. Since infants are not accountable, and b/c the atonement has already accounted for original sin, infants do not need to be baptized. When we become accountable and are enticed by the devil to do evil, we inevitably sin and therefore the commandment was given to be baptized only when we are accountable.
Christ was baptized when he was accountable b/c the commandment was given and he was enticed by the devil to do evil. Christ is the only exception to the inevitability of sinning, presumably b/c of his uniquely extra-mortal birth, so he is the only one who was enticed by the devil and did not sin.
How do infants progress?
One problem with this view, as illustrated by this post by Mark Butler (as well as others), is how to understand the plan of salvation as it pertains to infants who die before the age of accountability. Can they eventually be exalted without being baptized? Will they ever sin? If so, why wouldn't they have to be baptized too? If not, how come they can progress to exaltation without ever having to pass through the process of sin and redemption like the rest of us?
I think what's most consistent with what the scriptures actually say (I'm most interested in doing theology that is based on the canonized scriptures (putting less stock in other prophetic quotes) is the view that infants will eventually have the possibility of being exalted without ever having to be baptized b/c these souls will never be enticed by the devil to sin. They will have to learn and grow, but they will not sin per se in the sense that the rest of us who reach the age of accountability will sin by choosing the enticements of the devil over the commandments of God.
One implication (or at least related idea) is that Lucifer's negative answer to Eve's rhetorical question "is there no other way" is a lie. That is, there is another way, and that other way is the path that infants will tread.