Indeed, when we consider the data of this text on its own, it is modern forms of credobaptism, not paedobaptism, which actually struggle to align themselves with the exegetical details. Colossians 2:11-12 fits into the NT norm of baptism being part and parcel of conversion as the initiatory rite of the faith. Salter quotes with apparent approval Moo’s position that ‘baptism is the instrument through which we are buried with [Christ],’ and Salter states, ‘for Paul, baptism effects a vital union with Christ.’  It is not clear to me what meaning words such as ‘instrument’ and ‘effects’ have in the modern varieties of credobaptism, where baptism is subsequent to conversion, sometimes after several years, and perhaps only following a period of interview and assessment by the leadership of a church. In theological terms, it appears that the covenant sign of justification has become a functional sign of sanctification.

 
Do you see what he did there? He argued (correctly) that if Col 2:11-12 means anything, it means that we are buried with Christ, and raised with him, in baptism – so if a credobaptist sees baptism as something which takes place after conversion, rather than as part of conversion, then he’s made even more of a mess of Colossians 2 than the paedobaptists. (Though I doubt he’d put it like that.)
 
He’s right. Even though I get more riled-up responses from church leaders on this than on anything else I teach, I just can’t get away from it in the texts: Paul says that we are buried and raised with Christ in baptism (Col 2:11-12), and united with Christ in baptism (Rom 6:1-5), and that we put on Christ in baptism (Gal 3:27). (“Heresy! Justification is by faith alone! Heresy!”) Peter, not to be outdone, says that baptism is one of two things we do to receive forgiveness of sins and the Holy Spirit (Acts 2:38), and even says (in 1 Peter 3:21) that “baptism now saves you” (“Heresy! What about the thief on the cross? Heresy!”) So if believers’ baptism is to make any sense at all, we cannot keep articulating it as if baptism doesn’t really do anything, but merely represents something that has already happened. That sort of thing, as Gibson points out, is an epic credobaptist own goal: it’s so exegetically ropey that it probably makes more people paedobaptists in the long run.
 
Basically, you have three options when handling Colossians 2:11-12:
 
1. Baptism happens as a baby, but it doesn’t do anything. Being buried with Christ, and rising with Christ, both happen many years later.
2. Baptism happens after conversion, but it doesn’t do anything. Being buried with Christ, and rising with Christ, happen many weeks, months or years earlier.
3. Baptism is part of conversion, and it most decidedly does something. Being buried with Christ, and rising with Christ, happens in baptism, through faith.
 
And although David Gibson hasn’t shown the plausibility of #1, he’s certainly shown the implausibility of #2.
 
Let the rock-throwing commence!