Moreso when a writer - particularly one living alongside the rest of us in the twenty-first century - calls it "densely researched and thoroughly documented," as James McBride, a Church of God minister in the United Kingdom, does in this article.
The Two Babylons was a piece of creative anti-Catholic invective written in an age when certain sects of Protestantism could hardly bring themselves to regard Catholicism as Christian. The final edition appeared in 1919, though it first appeared as a pamphlet as far back as 1853.
Fifty or so years ago an American evangelist named Ralph Woodrow vigorously promoted Hislop's arguments through his own 'evangelistic association'. Then the unthinkable happened. Someone confronted his dogma with a few pertinent facts. Woodrow, to his everlasting credit, did a 180 degree turn, withdrawing his popular 1966 book, Babylon Mystery Religion. He wrote:
"As a young evangelist, I began to preach on the mixture of paganism with Christianity, and eventually I wrote a book based on Hislop, titled Babylon Mystery Religion (Ralph Woodrow Evangelistic Assn., 1966). In time, my book became quite popular, went through many printings, and was translated into Korean, German, Spanish, Portuguese, and several other languages. Hundreds quoted from it. Some regarded me as an authority on the subject of "pagan mixture." Evan the noted Roman Catholic writer Karl Keating said, "Its best-known proponent is Ralph Woodrow, author of Babylon Mystery Religion".It seems some modern writers have still to catch up with Ralph Woodrow.
"Many preferred my book over The Two Babylons because it was easier to read and understand. Sometimes the two books were confused with each other, and once I even had the experience of being greeted as "Reverend Hislop"! As time went on, however, I began to hear rumblings that Hislop was not a reliable historian, I heard this from a history teacher and in letters from people who heard this perspective expressed on the Bible Answer Man radio program. Even the Worldwide Church of God began to take a second look at the subject. As a result, I realized I needed to go back through Hislop’s work, my basic source, and prayerfully check it out. As I did this, it became clear: Hislop’s "history" was often only an arbitrary piecing together of ancient myths."
Wikipedia even has an entry on The Two Babylons, and while Wikipedia may not always be the best place to go for a serious discussion of theological issues, it has a very fair summary in this case.
"It has been generally regarded by scholars as discredited, with one calling it a "tribute to historical inaccuracy and know-nothing religious bigotry" with "shoddy scholarship, blatant dishonesty" and a "nonsensical thesis"...It speaks for itself that an organisation like Chick Publications continues to sell this discredited material, even labelling it "a classic." In other words, Hislop is the refuge of dilettantes, and there is zero excuse for anyone, conservative Bible believers included, lending credence to nonsense of this sort.
"Although scholarship has shown the picture presented by Hislop to be based on a misunderstanding of historical Babylon and its religion, his book remains popular among some fundamentalist Protestant Christians. The book's thesis has also featured prominently in the conspiracy theories of racist groups..."