If we don't discount the future, we run into mathematical difficulties. The first rule of utilitarianism ought to be KIFS - Keep It Finite, Stupid.

http://lesswrong.com/lw/n2/against_discount_rates/

The idea is not really that you care equally about future events - but rather that you don't care about them to the extent that you are uncertain about them; that you are likely to be unable to influence them; that you will be older when they happen - and so on.

It is like in chess: future moves are given less consideration - but only because they are currently indistinct low probability events - and not because of some kind of other intrinsic temporal discounting of value.