I try to imagine how mankind might have evolved without religion. It seems to me that all religion has done, is impeded science and done its best to bog us down in the dark ages forever. Luckily for us, science and rational thinking have snowballed for the past few hundred years and now religion is the annoying kid in the supermarket being dragged by mom and dad, desperately scratching its nails on the floor, screaming out its demands. Though quite a big kid.
I asked the internet 'What has religion done for mankind?' One of the first pages was Yahoo Answers (which I'm not a massive fan of). I opened it, and lo and behold! A comprehensive list of what it has done, and continues to do. A few odd ones are not so major (e.g. children growing up without music) but other than that, most major ones are covered.
(credits to RickK and Dreamstuff)
The demonization of other religions, e.g. Christianity demonizing Pagans ("They're devil-worshippers!"), the Romans demonizing Christians ("They're atheists and cannibals!").
Vilification of homosexuality, resulting in discrimination, parents disowning their children, murder, and suicide.
People and animals sacrificed as an offering to gods.
Food destroyed because it doesn't comply with specific religious beliefs.
Women treated like second class citizens, or even slaves, based on religious teachings.
Children growing up without music.
Children growing up to hate and fear science and scientists, because science disproves their parents' religion - leading to appalling scientific illiteracy.
Tens of thousands tortured and killed as witches (a practice which still continues today).
Millions of cats killed in the belief that witches use them as familiars, leaving rats free to spread the black death throughout Europe, killing millions of people in turn.
People bothered and sometimes woken up by door-to-door religion salespeople.
People dying because they believe their faith makes them immune to snake venom, or other lethal aspects of reality.
People dying - and letting their children die - because their religion forbids accepting medical help.
People choked, starved, poisoned, or beaten to death during exorcisms.
Female genital mutilation endorsed by religious texts, mutilation that results in infection, sterility and death.
Psychological and physiological conditions blamed on demons, preventing believers from seeking medical care.
People disowning family members for leaving their religion, in some cases symbolized by mock funerals.
Friendships and romances severed or never started over religious differences.
"Abstinence-only" sex education, resulting in five times the amount sexually transmitted diseases and teenage pregnancies - often leading to ill-fated "emergency" marriages.
Campaigns against safe sex, with similar results - responsible for much of the AIDS epidemic in Africa.
Religiously-prompted fear of polio vaccine, which halted the global eradication effort and brought polio back to many countries.
Women having septic abortions -- or being forced to have unwanted children they resent -- because religious organizations have gotten laws passed making abortion illegal or inaccessible.
Censorship (often destructive) of speech, art, books, music, films, poetry, songs and, if possible, thought.
The discouragement of rational, critical thought.
Believers whipping, impaling, poisoning or crucifying themselves during religious festivals as a demonstration of their faith and piety.
Children spending the period of their lives when the brain is most receptive to learning new information reading, rereading, and even memorizing religious texts.
People who believe the world is about to end neglect their education, are not financially responsible, and in extreme cases take part in mass suicides.
Environmental issues ignored because of beliefs that God will magically fix everything.
Wives told they will be tortured forever if they leave their abusive husbands.
People in times of trouble relying on advice from religious leaders without any sort of training in counseling or therapy.
Holy wars - followers of different faiths (or even the same faith) killing each other in the name of their (benevolent, loving and merciful) gods. (IN THE MILLIONS)
The destruction of great works of art considered to be pornographic/blasphemous, and the persecution of the artists.
Persecution/punishment of blasphemers (Salman Rushdie still has a death sentence on him), and blasphemy laws in general.
Slavery condoned by religous texts.
Children traumatized by vivid stories of eternal burning and torture to ensure that they'll be too frightened to even question religion.
Terminal patients in constant agony who would end their lives if they didn't believe it would result in eternal torture.
School boards having to spend time and money and resources on the fight to have evolution taught in the schools.
Persecution of Heretics/scientists, like Giordano Bruno (burned at the stake) and Galileo Galilei.
Blue laws forcing other businesses to stay closed so churches can generate more revenue.
Your need to pay more personal income taxes because religious organizations are exempt.
Mayors, senators, and presidents voted into office not because they're right for the job, but because of their religious beliefs.
Abuse of power, authority and trust by religious leaders (for financial gain or sexual abuse of followers and even children) - but hey, atheists are the immoral ones.
People accepting visual and auditory hallucinations unquestioningly as divine, sometimes with fatal results.
Suicide bombers, who are certain they will be rewarded in heaven.
Discrimination against atheists, such as laws stating they may not hold public office or testify in court.
Missionaries destroying/converting smaller, "heathen" religions and cultures.
Hardship compounded by the guilt required to reconcile the idea of a fair god with reality ("why is God punishing me? What have I done wrong? Don't I have enough faith?").
Human achievements - from skillful surgery to emergency landings - attributed to gods instead of to the people actually responsible.
Mother Teresa, prolonging the agony of terminal patients and denying them pain relief, so she can offer their suffering as a gift to her god.
Suppression of logical and critical thought. (very similar to discouragement of rational, critical thought seen earlier)
Billions spent to build, maintain, and staff houses of worship.
Grief and horror caused by the belief that dead friends and family members are tortured as punishment for disbelief.
Opposition to scientific (especially medical) progress on religious grounds.
Whole societies divided by minor differences in belief or doctrine, often resulting in violence.
Natural disasters and other tragedies used to claim God is displeased and present demands to avoid similar events (it's like terrorism, but without having to plan or do anything).
The unchecked use of fear and maintenance of ignorance to keep the population "faithful".
The attempted genocide of followers of a particular faith (e.g. the Jewish Holocaust, "ethnic cleansing" in former Yugoslavia).
Vilification of this current life as base and sinful when in fact it is fragile and precious.
Removal of responsibility for the planet and for the future because of apocalyptic beliefs that some divine being will either destroy it all or fix it all.
That was long. And for a good reason- religion has done a lot wrong. Unfortunately, it has done little right (excluding religious individuals who really do make Earth a slightly better place).
Maybe Galileo would have landed on the moon, and right now you would be reading this from a well populated Mars. One thing I can tell you is that we're both going to miss out on that. Oh wait, there would be no atheism since there would be no religion either.
Thanks for bothering to read all the way down to here :D