I basically do not oppose pay fee to Tx, not only protect network , but more important system should been a healthy that can gain enough money to supply high level service .
but we would consider how high fee can get more .
There is a relationship between fee and number of Tx
Vertical axis is number of Tx , and the horizontal axis is fee , so the area is the how many total fee (include referral program income ) system gain.
the left drawing show , charge high fee ,but a small number of Tx, so the income of system is small
the middle drawing show charge low fee , there a big number of Tx , but the income is also small
the right drawing show charge fit fee ,and the number of TX is a little lower than system capacity ( bts design is 100,000TPS ) , system get Max income
what position we are , I think is left drawing .