Herman Bavink acknowledges the flaws that exist in true churches,
Even though there are unbelievers within a body of believers and there remain impure elements in doctrine or practice, this does not disqualify a church body altogether. A true church in an absolute sense is impossible on earth. For that matter, neither can a wholly false church exist; to qualify for that description, it would no longer be a church at all. The “real” church in history is not perfect but, rather, has an undeniably dark side to it. The church is rent asunder by schisms and divisions, some going back to the apostolic era. At the same time it is a mistake to reject all diversity in the church. In unity God loves diversity.
Bavinck, Herman. Reformed Dogmatics : Volume 4