However, if block size is increased, there's really no reason why most miners won't include as many transactions as possible, since it doesn't really cost them anything. Transactors will no longer be required to pay to have their transactions included in the blockchain, and eventually profit-seeking miners will leave.
It costs mining pools nothing *now* to process transactions. And in fact they are not even required to fill blocks up with transactions,
there are empty blocks produced all the time.
Minimum fees can be set regardless of block size.
I don't think, that is true. Looking at the last blocks, they all had transactions in them.