What I am proposing may seem simplistic to some readers. However, I think this may be a way for the church to be united through baptism.
I'm beginning with five assumptions/beliefs:
First, Christ's church should be united around the gospel. This is commanded and easy to understand in the bible. Therefore, we should only separate from those who reject first order (gospel-centered) doctrines.
Second, second order doctrines are not biblical. All doctrines fall into either the first order or third order categories.
Third, baptism is not an issue to divide over. It should be treated as a third order doctrine. We ought to recognize that many Christians differ in opinion over the meaning of this sacrament; this should cause humility in how we interpret the meaning of baptism.
Fourth, all Christians should engage in "theological triage." We must recognize which doctrines fall into the first and third orders.
Fifth, unity does not require uniformity of belief and practice.
Based on these assumptions, how does this actually play out in the life of the local church?
Here is an idea:
We must understand that those who hold to infant baptism believe differently about the meaning of baptism than those who hold to believer's baptism. To be very simplistic, those who practice infant baptism believe that it is a sign of God's faithfulness to His covenant (and corresponds to OT circumcision). Those who practice believer's baptism believe that it is an act that shows the believer's identification with Jesus Christ in salvation.
These are clearly different meanings for the sacrament/ordinance.
While treating baptism as a third order doctrine, those in a local body will accept that both infant baptism and believer's baptism will occur within the church body. This does not mean that everyone has to agree on the meaning, but that they will accept the fact that it will occur. As for infants, parents could baptize them as the church gathers. Those who disagree with this practice could be there, but this does not mean they agree with or support the act. They key is that unity remains.
On the flip side of the coin, some parents in the body will not baptize their infants. Instead, they will wait until their child is saved, and then discuss with them when it is appropriate for them to be baptized as a believer. Those in the body who support infant baptism, while not agreeing with the waiting to baptize infants, will nonetheless remain united.
This same thing happens in other doctrines. Eschatology is a great example. I've heard many sermons where the pastor preaches something I disagree with. I don't dis-fellowship with the church family because of this. Just because I am present does not mean that I agree with all he has said.
I've been in situations where most of the people in a church hold to an Arminian position regarding salvation. While I disagree, I don't immediately break fellowship because of this difference.
I could go on and on. The point is that we don't stop fellowshiping over third order doctrinal differences. If we treat baptism in this way, we will remain united while at the same time holding some differences in interpretation over the meaning of baptism.
I realize that this will require much discussion, much listening, and much humility. Let's do it.