Exponential discounting with a discount rate that has a positive lower bound for all time makes perfect sense if you assume that there is always an opportunity cost to immediate consumption. Indeed this has been true for all of human history... and prehistory, ever since the first protoman discovered that sharpening rocks and weaving baskets instead of hunting and gathering now now leads to much better hunting and gathering later. But there are reasonable assumptions (e.g. "the universe is finite") that would prevent it from being true forever. On the other hand, I think most of those assumptions would also preclude the possibility of infinite torture. Is that what's happening here? Your intuition is effectively telling you "infinite torture is impossible", so you're willing to look at the other side of the bargain?