Dennis Prager answers in the affirmative:
For at least the last hundred years, the world’s most dynamic religion has been neither Christianity nor Islam.
It has been leftism.
Most people do not recognize what is probably the single most important fact of modern life. One reason is that leftism is overwhelmingly secular (more than merely secular: it is inherently opposed to all traditional religions), and therefore people do not regard it as a religion. Another is that leftism so convincingly portrays itself as solely the product of reason, intellect, and science that it has not been seen as the dogma-based ideology that it is. Therefore the vast majority of the people who affirm leftist beliefs think of their views as the only way to properly think about life.
While I agree with the rest of Prager's column, I have trouble with his characterization of leftism as a religion.
It is true that leftism is like a religion in certain key respects. But if one thing is like another it does not follow that the first is a species of the other. Whales are like fish in certain key respects, but a whale is not a fish but a mammal. Whales live in the ocean, can stay underwater for long periods of time and have strong tails to propel themselves. Just like fish. But whales are not fish.
I should think that correct taxonomies in the realm of ideas are just as important as correct taxonomies in the realm of flora and fauna.
Leftism is an anti-religious political ideology that functions in the lives of its adherents much like religions function in the lives of their adherents. This is the truth to which Prager alludes with his sloppy formulation, "leftism is a religion." Leftism in theory is opposed to every religion as to an opiate of the masses, to employ the figure of Karl Marx. In practice, however, today's leftists are rather strangely soft on the representatives of the 'religion of peace.'
Or you could say that leftism is an ersatz religion for leftists. 'Ersatz' here functions as an alienans adjective. It functions like 'decoy' in 'decoy duck.' A decoy duck is not a duck. A substitute for religion is not a religion.
An ideology is a system of action-guiding beliefs. That genus divides into the species religious ideologies and nonreligious ideologies. Leftism, being "overwhelmingly secular" just as Prager says, is a nonreligious ideology. It is not a religion, but it shares some characteristics with religions and functions for its adherents as a substitute for religion.
You might think to accuse me of pedantry. What does it matter that Prager sometimes employs sloppy formulations? Surely it is more important that leftism be defeated than that it be fitted into an optimal taxonomy!
Well yes, slaying the dragon is Job One. But we also need to persuade intelligent and discriminating people. Precision in thought and speech is conducive to that end. And that is why I say, once more: Language matters!