I think it serves as kind of a rallying cry. The radically fissiparous Protestants still find union in lies about Catholics. Misstating Catholic teaching brings them together as nothing else can.
When all else fails, they can always agree that Rome is the source of all evil and is always wrong. And if Rome seems right, see the preceding sentence.
Like angry children who get together occasionally only to swap stories about nasty their parents were ... stories which wander further and further from reality.