I know it's an unfair comparison, and I know it's like comparing apples and oranges, but I can't really articulate the problem with holding people to that kind of biblical example when discussing the church.
Of course we don't quote scripture when defending orthodoxy and traditional, confessional Christianity. It's not biblical apologetics. The bible was written before the church was organized, so there's not a whole lot of scripture to quote in these sorts of discussions.
Other than the 7 churches of Revelation, there's not much guidance there when it comes to ecclesiastical questions, so, naturally, we don't quote the scriptures much.
Now, if you wan't to hold a theological debate, we'll quote you some scripture! HA! and some confessions, and some scripture, and some catechitical writings, and some scripture, and some church fathers, and . . .
I consider Catholics and Protestants to be just as true a Christian as an Orthodox. But when it comes to claims that some Protestants practice some sort of pure or stripped down version and thus more "authentic" Christianity then they run up against the wall of orthodox (small "o") Christian historical development.