It is exactly the opposite.
They agree in machinery; almost every great religion on earth works with the same external methods, with priests, scriptures, altars, sworn brotherhoods, special feasts.

They agree in the mode of teaching; what they differ about is the thing to be taught.

Pagan optimists and Eastern pessimists would both have temples, just as Liberals and Tories would both have newspapers.

Creeds that exist to destroy each other both have scriptures, just as armies that exist to destroy each other both have guns.
The great example of this alleged identity of all human religions is the alleged spiritual identity of Buddhism and Christianity.

Those who adopt this theory generally avoid the ethics of most other creeds, except, indeed, Confucianism, which they like because it is not a creed.