Because of this tendency, I often shy away from arguments against Catholicism that take as their launching point the various abuses and aberrations of the church throughout the centuries, as if the Protestant's only problem with Rome is the occasionally opulent pope or abused altar boy. In other words, a robust Reformed argument against Rome would focus not only on what it became, but also on how it began.
If all we focus on are the incidentals, then is not this a tacit admission not only that the solution to Rome is not Protestantism but reformed Catholicism, but also that our entire ecclesiology is a convention arising post hoc, a reaction to biblical Christianity gone awry instead of a return biblical Christianity itself? Don't miss the import of what I'm saying: if we focus solely upon Rome's abuses, we are surrendering not only all exegesis, but also conceding that Jesus did in fact intend to found a visible church characterized by apostolic succession and Petrine primacy, but once that church messed things up, we came along with a bunch of new ideas about invisible churches and Sola Scriptura.
To put it bluntly, Protestants need to argue for Protestantism, not just against Catholicism, and we need to do it from Scripture, as if (gasp!) Jesus actually intended something akin to Reformed ecclesiology all along. Why would we be comfortable with anything less? I mean, what are we, Protestants or simply non-Catholics?
So let's not shoot ourselves in the foot by just settling for cake. Let's go the next step and demand to eat it, too.