Nothing in life has yet shown me that it must absolutely be attributed to a higher intelligent power. There are things that can't be explained, but there have always been things that can't be explained. Many of them which were explained by God in the past have been shown to be perfectly natural, and to fit into patterns described by science. So why not assume that other things that can't be explained yet, won't some day be explained by science in very human terms?
The things for which we still don't have answers aren't even best explained by a god. For instance, the creation of the universe. It's natural to assign that achievment to some higher power to explain it away. The problem is then, who created that "God" which created the universe? It doesn't end up answering the question, only bringing up the same one again, or new ones.
I can also see a logical progression of religion through the ages, all stemming from humans' desire to explain things. I see no other reason for religion to exist, but science seems to have taken over that job now, which leaves me with no more use for religion.
There is so much more to it, but that's the main part.