IMO the block reward reduction "singularity" is one of the only real design flaws in Bitcoin.

Halving the reward in one shot will create an incentive for rational, profit-maximizing miners
to organize a 51% attack on the network, to maintain or even increase their mining profits
through evil means.

This possibility exists even today of course, but miners seem a lot more likely to organize and
attack right after (or right before) the mainstream network kicks them in the nuts
by halving the reward.

Maybe we will see a fork of BItcoin, which keeps the block reward at 50BTC, with a very high %
of the mining power moving to that - basically playing chicken with users to try
to make them switch to the 50BTC-for-life fork, by reducing the hashrate on the 25BTC
network to the point where someone else can 51% attack it.

To minimize these risks - the block reward should have been constant, or reduced gradually,
a little bit each block. People are less likely to notice, protest, and organize
against a gradual change. That is how governments become increasing large and oppressive,
fiat currencies become increasingly worthless, etc.

-rph