To understand Bataille, it pays in any case to have read some Nietzsche, Marx, Hegel and Freud, since he draws a lot from these. Visions of Excess has a simply premise from Nietzsche, that when we are unhappy we lose all moderation and go into excess. Another Nietzschean premise is that those who a psychologically rich can afford to go into excess more than those who are psychologically impoverished. So it is that Bataille tries to appeal to a particular segment of society -- those who have been made to feel unhappy by their lack of power in relation to society's hierarchical structure, but who are nonetheless intrinsically rich enough, within themselves, to express a different kind of spirituality than those who are on top.
VISIONS OF EXCESS contains short meditations, some of them pornographic, but all of them in relation to the structure of psychology I have described. He sees society as a body, with the lower parts being more important than generally assumed. He likes the idea of a body without a head. He also likes the idea of challenging oneself with greater and greater forms of evil. This is a Nietzschean conception, that incorporating more evil into the consciousness expands the psyche in a beneficial way.
As Bataille points out in his short essay, there would have to be two "suns" for us, if we were to process the story of Icarus in accordance with what most people believe (falsely) about the nature of reality. Our priests throughout the ages have taught us to bifurcate reality, so that loss, decline and deterioration do not seem to be part of the essence of humanity at all.
The climbing to the height is one thing, and it is understood as a representation of one kind of reality. Let us call it will to power and ascendence through the ranks of homogeneity.
Then there is the cry of alarm, the melted wings and the terrifying falling, away, away from the sun. This registers to our socially conditioned minds as a state of heterogeneity. It registers as discordance, as formlessness. We are alarmed because we implicitly believe the possibility of continuing to ascend to heaven to be infinite. We relegate all fallen heroes to the parade of shame which is populated by those whom we consider to typify those elements of disruption and shame (the heterogeneous) who have no place in well-ordered society.
There is a certain point in Icarus' journey when upwards starts to become downwards. What was ecstasy becomes grief. To a compartmentalising mind, there can be no association between the spiritual (or psychological) pathway towards ecstasy and the one which leads to grief. They are two different pathways, with two different results. Thus, the bifurcation of the mind, which demands two suns, for Icarus's falling to the Earth is also a falling into the sun, to be burnt alive by human demands that prohibit a failure of any sort.
Bataille's insight is that loss can also be a gain, a thrill, a mode of ecstasy, for it is part of life: Indeed, there is only one "sun" (one realm of human experience), and Icarus is falling into it.