Assumption #1: There is no free will - all of our decisions are all determined by the causal web of biology and environment.*
(*note: determinism will heretofore be defined in the context of human consciousness outcomes, such that human thought be considered determined by events beyond one's control, even if other, non-strictly-deterministic forces may be at work at the atomic or super-atomic level.)
Taking only that assumption as a baseline proposition, one runs into profound implications both at the individual and societal level. Because the notion of determinism seems contrary to common sense, and until only relatively recently has a large body of evidence been gathered to support it, we have a large infrastructure of cultural and civic institutions that operate with the assumption that we are each rational agents, responsible for our individual choices and actions. In our personal lives, we also operate under this assumption. Our concept of self, as well as that of others, is predicated on the seemingly obvious notion that we are the originators of the good or bad choices we make.
In Western religion, the concept of free will is the fundamental basis for the determination of one's fate in the afterlife. There is a black and white distinction between choices, and one is ultimately held accountable for one's decision. Contrast this with the East, where the concept of reincarnation transcends individual choice, and assumes a fatalistic process whereby one's very existence is predicated on the notion that bad choices will be made, and not until one has learned the correct path may eternal reward be found. This does not however completely shut the door on free will, as one could certainly insert an ad hoc "soul" into the bio/enviro equation. But the fundamental frame work is at least much more forgiving to the prospects of determinism. For the purposes of this discussion, and as I am certainly a Westerner, I'll keep to the political, cultural and religious implications for Western society.
Religion is difficult to fit into this discussion, as it is split rather sharply by two interpretive experiences - the sacred/emotional and profane/rational. Our discussion is at its root one of logical inference and scientific data, not common sense or intuitive knowledge. Indeed it is at the experiential level that we had thus far received the illusion of free will, and now having renounced it from the onset we curry in as much reason and as little intuition as possible. Yet casting away the sacred knowledge of experience, we are left only with the cold profanity of reason. And this makes for poor religion. So one finds it difficult to continue to carry religion onwards, in strictly materialist fashion, when our subject has reached such a limited conclusion.
Or has it? Just as a liberal mind might find ways to let religion in through the cracks and bars of scientific materialism, allowing it to serve as a sort of placeholder for the unknowns within the knowns, so might it be possible to let some religion in here. As an atheist, however, I'll have to allow others to interpret the religious implications of determinism.