|I have, and things wouldn't be any better.|
I think that's a naive attitude. Just as all of religion's positive effects (charity, volunteering, community, etc.) could easily come from secular sources, isn't the same true of the evils it has produced? Is belief that you are acting at the behest of an almighty spirit necessary to torture dissenters? To enslave and/or rape those weaker than you? To ritualistically starve your children or deny them medical treatment? To crash airplanes into occupied buildings?
I suppose it depends on how broadly you define "religion"; should it include cults of personality? We've seen people do some awful things in the name of charismatic leaders, never applying a skeptical mind to their sovereign's claims.
Officially, most North Koreans are nontheistic, but is the Juche philosophy really so different from a religion apart from its answer to the "god" question? The Dear Leader promotes an air of veritable divinity around himself even as his country's citizens starve, and he need not appeal to a higher power to keep it that way.
Religious obedience, or tribal loyalty?
Even religious fanatics like the Muslim extremists assaulting and killing non-Muslims in the Middle East are not too dissimilar from criminal gangs; it's tribalism in its most extreme form. We see its benign cousin every time there's a major sporting event, though the disdain that one team's less sportsmanlike fans express toward the opposing team tends to subside after the game (the violent and destructive episodes of football hooliganism being a notable exception). Belief that violence against the "other" makes some invisible being happy is unnecessary; it only requires pent-up anger, often brought on by socioeconomic factors, to be channeled as hatred toward another individual or group.
Now there's the matter of suicide terrorism. The promise of an eternal paradise after death is certainly a useful tool for convincing people to sacrifice their lives, but is it the only way? I think it's entirely possible for someone who accepts that death is followed only by the end of consciousness to willingly die for what they think is a good cause.
If you were utterly convinced that your people were at war with an entire civilization, a monolithically evil enemy whose every member was like a worker wasp supporting the nest you want to destroy, could you be persuaded to commit a kamikaze attack that would take out thousands of them? Would you need to believe you would be rewarded for it in the afterlife, or would it be worth it solely to aid in the defense of your loved ones back home? It's really only necessary to unquestioningly hate those you perceive as enemies, to believe that every last one of them deserves to die, to carry out an attack like 9/11.
A disease, or merely a symptom?
Christopher Hitchens claims that "religion poisons everything"; I can't help but wonder if it's analogous to potassium cyanide sprinkled atop the arsenic cocktail we'd be drinking anyway.
Perhaps a better analogy is that many atheists see religion as a disease when it may well be merely a symptom of other ills to which the human mind is inherently susceptible. I'll dare to assume that most people are not skeptics, and even people who consider themselves skeptics are fighting an uphill battle against their own desire for certainty. This gives the masses a tendency toward blind obedience of authority, whether that authority is a manufactured deity, an ideology, or an individual psychopath.
Even if religion vanished overnight, we'd still have no shortage of man-made problems. Hateful people create hateful gods in their own image, and those people would remain hateful even without their imaginary friends egging them on.