I have a Catholic friend who sent me the link to this essay (though she warned there are a lot of typos from whoever webbed this). Peter Kreeft had been Protestant and converted to Catholicism, so he has an interesting take. (I was raised Catholic and currently consider myself Protestant so that’s why this is particularly intriguing to me.) An excerpt:
There are at least four things wrong with the sola scriptura doctrine. First, it separates Church and Scripture. But they are one. They are not two rival horses in the authority race, but one rider (the Church) on one horse (Scripture). The Church as writer, canonizer, and interpreter of Scripture is not another source of revelation but the author and guardian and teacher of the one source, Scripture. We are not taught by a teacher without a book or by a book without a teacher, but by one teacher, with one book, Scripture.
Second, sola scriptura is self-contradictory, for it says we should believe only Scripture, but Scripture never says this! If we believe only what Scripture teaches, we will not believe sola scriptura , for Scripture does not teach sola scriptura.
Third, sola scriptura violates the principle of causality: that an effect cannot be greater than its cause. The Church (the apostles) wrote Scripture, and the successors of the apostles, the bishops of the Church, decided on the canon, the list of books to be declared scriptural and infallible. If Scripture is infallible, then its cause, the Church, must also be infallible.