[politician]

As I understand it, the goal of this feature is to drive miners to begin charging transaction fees to mint blocks rather than rely on the reward built into the protocol. The reward was designed as a carrot, but eventually it'll give way to transaction fees. If you study the protocol, transaction fees are built in; early on, however, they weren't used (i.e. spending BTC was free).

However, there is a more interesting question about transaction processing rates and competitiveness. VISA claims processing rates of 10000 transactions/second. BTC is at around ~700 transactions/second.

If you want to learn more, here are some links:

Transaction Fees and Rates https://bitcointalk.org/index.php?topic=1314.msg14748#msg147...

Scaling Goals https://en.bitcoin.it/wiki/Scalability

[Retric]

The problem boils down to this, suppose total bitcoins where worth 1 billion dollars, an average day exchanged 1/10th of that or 100 million dollars worth of transactions. Now suppose a 1% fee per transaction that's 1 million dollars worth of computing power per day or ~41k per hour (assuming mostly rational actors). Now suppose it costs 10x that or 410k per hour to take over the network. Well the 'pot' is worth 1 billion so that's a clear win and someone would do that.