Firstly that is not how evolution is generally taught. Secondly, Atheists would be a relatively small subset of the group "people who believe in evolution", there would be a big subset who are also christians, another big subset who are buddhists and so on. THere are probably more christian...
note that death is not required - just differences in reproduction rates. If you have a gene that results in you having greater than the average number of surviving, breeding offspring, then that gene will spread in the population.
no, it doesn't really. Sexual reproduction increases the pool of genes, and means that if you don't have the genes to survive a certain situation, but another individual does, then you can mix genes and then more of your own genes have a chance of being in a body alongside genes which help them...
humans are generalists, and in the long term that's undoubtedly the best position to be in. Species that adapt too well to a specific environment are at danger of being driven extinct if the environment changes in a way they cannot cope with - the more extreme the adaptation, the easier...