I would say that while humanity would be better off without religion, It's just not possible. Even if you remove deity based belief structures such as christianity or islam, people will just find something else to turn into a religion. Just look at what happened to socialism, or oprah for that matter.
In my eyes, a devoted trekkie and a devout christian are the same type of person. They have both deified an allegorical work of ficton. Both canons have significant inconsistancies, and violate several accepted laws of nature, explaining them away with ("my god can do anything", or "in the far future we can do anything"). But that doesn't stop people from dressing up as klingons or murdering their neighbors as part of a sanctioned mob*.
The main difference, is that at least the people obsessed with buffy or stargate know that their idolized story is fake (at least, most of them). Religions tend to have real historical figures(though exagerated), several centuries of intertia and tradition, not to mention a variety of brainwashing during childhood, to back them up. somewhere between the two are cults and fad beliefs, which tend to have a veneer of history and tend to be the refuge of those people who would be willing to believe in a more mainstream religion but were unable to suspend disbelief for the one they were born into.
I would say that religions stem from two basic human factors. The fear of the unknown, and a form of behavioral inertia. On a very basic level, it is impossible for any one person to understand everything around them, even if all the information were available. Because of this humans make assumptions such as, the sun will rise tomorrow. But if you dont know much about the sun, you might wonder why, or even whether the sun would come up. Thoughts like that scared the hell out of our ancestors, so they filled in the blanks. A higher being must ensure the sunrise they decided, and religion was born. Which worked for a while, untill someone wondered whether that god would continue to ensure the sunrise, so they filled in the blanks again. the god must require nurishment in the form of sacrifice of resources or certain behaviors. So they began sacrificing and praying, etc, etc, etc, present day.
As you might expect from the results, once you get into the habit of explaining away scary unknowns and doubts with religion, it gets pretty hard to break the addiction. And if someone comes up with a contradictory explanation, the only way stop up the leaks it pokes in your dam is to either make your own religion more complex to explain the inconsistency, or to just kill the heretic before he causes irreparable damage (astronomers burning at the stake comes to mind).
A successor to religion is education which replaces the doubt with real knowledge instead of assumption.
Saddly, modern religions have grown so complex and all encompassing in their explanations, that every time a new bit of knowledge is discovered by humanity, it pulls another piece out of their Jenga tower of assumptions, threatening to cause the whole thing to keel over. And that would uncover the REALLY SCARY unknowns, like why are we here, what happens when we die, and what is stopping our neighbors from killing us in our sleep.
The end result of all this being that many religious groups treat knowledge like an enemy. And if we let them win and, stop learning where we are now, its only a matter of time before some cataclysm wipes us from the face of the universe.
If humanity is every going to survive as a species in the long term, religious groups are going to have to come to terms with the fact that their explanations of physical reality aren't needed anymore. because we now understand that the age of the world closer to 4.5 billion years than either eternal or only 6000. They should limit themselves once again to things that are currently beyond understanding, and stop slowing us down
*(several catholic saints as well as the founders of the protestant branch [ie Martin Luther] are documented as having lead pogroms to purge(murder) nonbelievers. Not to mention that strange obsession with witches who not only never existed outside of folklore but also are never mentioned in the original christian holy texts at all [the word that is commonly translated to mean "witch" actually meaning "sorceror" in both hebrew and the later greek texts].)