First of all, I'm an atheist, and I agree with every other atheist point that has been made in this thread. First, it is impossible to prove or disprove anything. Any random person could claim to be god, and nobody could ever disprove him. There is no way to prove solidly that that person is lying, no different than the fact that there is no way to disprove god. Everything that we know is derived from our own common sense- for all we know the fact that we need to breathe air to survive could be coincidence- what if people just have always happened to have heart difficulties just as they stop breathing for a second? If we ignore all of those previous points, there's one more thing I want to add: Even if there was a god, he would have to be such a horrible, evil, mean, hateful person that there is no reason he would be different from the devil. Think about it- he could just as easily put everyone is eternal bliss and prove that he exists rather than making us live our own lives (and for some reason wanting us to believe without giving us any proof). If any person were to cause as much death as god would have if we believe the bible (hurricanes, earthquakes, etc.), he would be the greatest mass-murderer ever.
According to Religious beliefs (not trying to throw myself at this so I can give an unbiased opinion), God gave us free agency. And he is perfect. Therefore if he did anything to take away our free agency, it would be a sin. He can't stop people from murdering people by controlling him. He didn't tell large armies to kill each other. If you blame people for killing eachother for their beliefs in God, then that's the same as blaming all racism against black people on the first african Americans. Or blaming hate against gay people on their parents (since it's apparently based of DNA, if I have been informed correctly). So you can't blame everything that goes wrong on God.
The reason God doesn't do that, according to most religions, is to test us. If we all lived in eternal bliss, it would be easy for people to be like, "Oh yeah, I'm totally nice, I wouldn't hurt anybody." Of course, in slightly worse circumstances, those people could become thieves, murderers, etc. Similarly, if God came right out and showed us that He exists, you'd have to be insane to commit any sins. So, those same people would, again, be nice people who wouldn't do anything to anybody. But all that would prove is that they could be bribed and manipulated by fear.
My point was that there is no reason in attempting to keep people out of heaven- if everybody were born without urges to commit crimes our world would probably perfect. Plus, you have to remember that my point doesn't apply to everyone- mostly to creationists for whom god plays a role in everyday life.