I think some people are too concerned with the theoretical differences between the religions and ideologies, and it blinds them from seeing the true similarities, or the true differences, that actually exist.
Theoretical differences may make two religions seem like polar opposites.
But if you look at the people, the concerns they have, the form of organization, the vocabulary, the assumptions about how often to meet, where to meet, what you do at a meeting, and so on, you may pick up on what is called de facto similarities.
If we look at de facto similarities, rather than the intangible theoretical differences, we will see that, for example, Scientology and Mormonism are very similar. Mormons don't believe in Thetans. Scientologists don't believe in Nephites. But so what ? Those beliefs are just that: beliefs. It is the actualities of a religion, the physical, tangible part of the religion, that really defines it. And when it comes to that, they are both modern, both originating and most successful in the US, both religions of the suit and tie, religions of the salesman, and very, very concerned with making money. Both have what are called "WASPs" as their primary target demographic for conversion.
Another example we could give is Nation of Islam. In theory, Nation of Islam is a form of Islam. But in reality, it is a development of the Afro-American form of Protestantism.