Readers are urged to consider that the following two positions of Satoshi are potentially mutually exclusive:

• Fees will support the system, long term
• Block size may be increased in the future

Right now, the block reward subsidy supports the entire system, so it is difficult to draw any conclusions about a fee-supported future -- and yet that is what we are being asked to do.

At the two extremes...

If the block size strategy is too loose (too big), there is no incentive to curb spam, there are not enough fees.

If the block size strategy is too tight (too small), fees are very high, in-blockchain traffic is discouraged, possibly users are discouraged away from bitcoin.

The open question is...
how to pick the best number?
or, how to enable a market to pick the best number?
or, how to pick an algorithm that picks the best number?

The fee/block-size balance is a crucial balance that must be maintained for the health of the system.  There is little evidence that Satoshi put much thought into this, probably supposing that the market would figure out the answer.