There are many different ways in which we could discount the future. The problem with almost all of them -- including the "hyperbolic" discounting Ainslie describes -- is not (necessarily) the mere fact that they discount, nor that they discount too much, but that they discount inconsistently: given times t1,t2,t3,t4, the relative importance of times t3 and t4 as seen from t1 is not the same as their relative importance as seen from t4. Or, to put it differently: if I apply t2-as-seen-from-t1 discounting together with t3-as-seen-from-t2 discounting, I don't get the same as if I apply t3-as-seen-from-t1 discounting.

It is possible to discount the future consistently, but there's basically only one degree of freedom when you choose how to do so. If you give events a time t in the future weight proportional to (constant)^t then that's consistent. It doesn't open you up to the bug ciphergoth describes, where your judgement now is that times t1 and t2 are almost equally important, whereas when t1 comes along you regard it as much more important than t2. (If you don't discount at all, that's the special case where the constant is 1.)

Ooo, no, actually you have more degrees of freedom than that: the most general scheme is that you choose a function F(t) and weight things according to that function. (Important note: one function, and its argument is absolute time, not time difference.) But the exponential case is the only possibility if you want your discounting function to be invariant if your whole life is shifted in time. (Which you might not -- if, e.g., there are external events that make a big difference.)

Anyway, the point is: it's not discounting "more than expected" that's the issue, it's having a pattern of discounting that's not internally consistent.