Comfort

[The Grand Nudger]

Edit:
Are atheists are too egotistical(like theists like to say) to let go of their personal comfort for the idealistic/perfect ideas of theism where everybody strive to get in heaven by doing "good deeds"? Is science is used just to guard personal earthly comfort by saying "It a scam there is no heaven".

There's nothing perfect about "the ideas of theism"..which, in and of itself is a bit of a misclassification.  There are ideas in theism, but the only idea -of- theism is that there is a personal god who intercedes in human affairs.  

Striving to do good deeds, for example, is a common human idea..but some brands of theism don't think that's what gets you into heaven anyway, and those that don't believe in heaven in the first place aren't doing good deeds to get into the great big divine after party.

Traditionally, diverging from religious claims hasn't exactly been comfortable for those that do it. Heretics and unbelievers weren't living in the lap of luxury for their lack of belief. That heaven is a scam was known long before science or christianity came along.  One of the oldest atheists of record was responding to hinduism:

There is no other world other than this;
There is no heaven and no hell;
The realm of Shiva and like regions,
are invented by stupid imposters.

-though it's difficult to believe that this, even, was the first time that someone realized it was bullshit. The earliest indication that anyone believed in an afterlife of any kind are red ochre burials..and even those seem to have been pilfered by people who didn't agree that Uncle Og needed that celt in the afterlife. The dead, they must have thought, chop less wood than the living.