Caveat: Today's topic can be a controversial one, so let me invite readers to come to it with an open mind. My intent isn't to pass judgment or challenge anyone's beliefs, but instead to explore the thought space in a new and hopefully insightful light. Feel free to take this perspective and incorporate it into your belief(s) however you see fit.
Why is it that a discussion of religion needs such a guarded introduction? Because these massive memeplexes are extremely fierce competitors for brain space, evolved over (in many cases) thousands of years. Consequently most of them seem to have developed strong defense mechanisms such as a deep emotional attachment to their core tenets, and a corresponding hostility to any outside challenges of the same. And these mechanisms do their job well: the best way to make sure we keep and spread our beliefs is to make sure we never seriously question them or consider alternatives.
But this defensive behavior isn't why I've taken to calling religions the "dinosaurs of the memetic world." The metaphor is rooted in their strategies of evolutionary competition: size and power. In both cases, natural selection seems to have reached a phase wherein the internal barriers to growth suddenly fell away, and a race to be the largest and meanest guy in town ensued. For religions, this may have happened when our language skills became developed enough to convey abstract concepts, and to persist ideas over significant time and distance (via written form). Whatever the cause, the result was clear: complex, highly integrated worldviews that were propagated as single atomic ideas. And thus the "isms" were born.
I don't have anywhere near enough background in comparative religions to attempt an analysis of what drives their memetic success. But a few things do jump out as common traits that, intuitively, should be selected for. Dogma is a good example: memeplexes that encourage you to unshakably trust a given authority (be it another human being or a book) effectively curtail a major source of lost converts. Encouraging the propagation of the belief system from parent to child is another obvious mechanism. The advantages of incorporating rewards for believers and punishments for non-believers require little explanation. And of course we can't forget evangelism, perhaps the most directly memetically beneficial trait possible. (It's intriguing to me that non-evangelistic religions exist at all, and this is surely a testament to evolution's creativity in finding niches to survive in.)
However, like dinosaurs, religions eventually reached a cap. Sooner or later the strategy of pure brute strength hits a wall, and nature starts looking for other ways to improve. In this way it might not be unreasonable to collectively call the Abrahamic religions the T-Rex's of the memetic world: refined machines for turning a human brain into a machine for copying the memeplex. But they do so without any great degree of subtlety, and their size and complexity leaves them slow and vulnerable. One could make the case that the last 400 years have seen the beginning of the next stage, in which the dinosaurs fall to a new generation of sleeker, more elegant competitors.
Just to be clear, I'm not arguing that these religions are necessarily "wrong" (although it would be pointless to deny that I personally am an atheist). However I hope most would agree that the ancient religions have accumulated a lot of baggage in their rise to dominance. The downside of a dogma is that once an idea gets itself incorporated it will tend to stick around for a while, even if it's not a very good idea to start with. At their core, religions are fighting to supply human beings with an answer to that most central question: Why? Why are we here? What's the point of all this madness we call our lives, our reality, our Universe? Religions which carry around prescriptions for daily life, once an asset in their propagation, suddenly find it an encumbrance when pitted against more concentrated modes of answering "why?"
Predicting the future is a good way to look foolish so I hesitate to venture into such speculation. But I can say what I'm hoping for, which is that evolution will work its magic: religions supply us with answers to the big questions, so the further they evolve, the better and more satisfying those answers should ultimately become. It seems like wishful thinking to suppose we'd ever find one religion compelling enough to close the debate, but if we can even reach a point where they're all close enough to co-exist then it would reshape our civilization. The dinosaurs may die, but something smarter and better will hopefully follow in their footsteps... let's just hope it doesn't take 65 million years this time around.