He has additional theological reasons (Purgatory, Marian doctrines, Papacy, icons, and “ambiguities” regarding justification and tradition) for staying put. But if these do not constitute reasons for believing that the RCC is a false church, then they also cannot trump church unity, can they? I still come back to the idea that if the RCC is a true church, then we ought to be a part of it. My own position is that the RCC is a false church because of these reasons (though I would not phrase the RCC position on justification as “ambiguous.” There is hardly any ambiguity in Trent’s doctrine of justification). They do not have the gospel. They twist the sacraments into something unrecognizable, and their version of church discipline is surely wide of the mark in the papacy. The marks of the church are therefore either so twisted as to be negligible, or else non-existent. The ultimate reason (for me) for not viewing the RCC as a true church is its own self-understanding as an extension of the incarnation of Jesus Christ. This is idolatry of the church. It is man worship, church worship. It takes what belongs only to Jesus and gives it to the church, despite its own claims that it does not do that.
– Lane Keister; A Response to Leithart’s “Staying Put”