Of course, the biggest problem in communities of faith is not incorrect doctrine, but a simple inability or lack of desire on the part of the adherents to believe the doctrine as established by the church(es) or to follow it in the practice of their lives.
When you come down to what the adherents believe, it is quite different than what the church(es) teach. For example, only 48% of Catholics believe that Jesus lived without sin according to a poll done by the Barna group. And "Buster" Christians (Proddy, I believe) were found more likely to try to avenge a perceived wrong than an average joe-on-the-street.
That is Satan's plan. Not perverting our doctrine. Or beguiling us with the ability of each of us to interpret Scripture. It's the simple apathy of getting caught up in what's best for us or what's easy. That, in my opinion, is far more dangerous than a few "mini-popes" running around (or even 30,000). And it affects all of us. Holy, Apostolic, and Catholic or not.
However, you are correct that a whole lot of people don't even follow the doctrine that they (officially) profess. Actually, it begins before that ... they don't even know the doctrine that they officially profess ... see your data about only 48% of Catholics believing Jesus lived without sin.
Catholic catechesis has stunk in this country since the early 1960's. And, unfortunately, we aren't the only ones who can make that claim.