How do you know what the “plain meaning” of a word is?

It depends on what your definition of the word “is” is. (JN)

And how do you reconcile this with the idea that Baptists and Presbyterians are both equally right about baptism?

Not what I said. Re-read, please. I never said that Baptists and Presbyterians were both equally right about baptism. I said that they both could back up their points of view from Scripture. We know that for one to be right is for the other to be wrong, but it’s one of those situations where we might never come to the correct interpretation. Hence, my viewpoint that it shouldn’t be a test of orthodoxy.

That being said, it is just fine, however, to hold to a certain position as a congregation or denomination, practice it, and require your elders to teach it and abide by it. But it’s not something Presbies should use to whack Baptists over the head with, and vice versa. My impression from personal experience is that it’s usually the credo-baptists who do the bashing, because most of them are against the flavor of covenantalism that paedo-baptism represents.

The funny thing is, paedo-baptist denominations uniformly also practice credo-baptism, when they baptize adult converts to the faith. The profession of faith that the PCA requires for an adult baptism is oddly similar to what SBC churches usually ask. I don’t know much about the Roman RCIA, but I expect that it’s a similar thing. So when somebody asks me whether I’m a credo or paedo baptist, it’s great fun to say “both!” :)