Those who go to a festival for the pub sessions and don't see why they should pay for a festival season ticket should try going to the same pub on a different weekend and see if it has the same ambience.

Festivals cost money to run, they require income. If not from tickets then from sponsorship and donations. If the publicans gave the festival a reasonable sum for the extra revenue the festival had created there may be a justification for the "free" fringe.