When you go to a show, you're supposed to discover something. Maybe it's a local band who you follow around for a couple years. Perhaps you learn that it really was the production on that demo and those guys are as good as everyone told you. Pay to play robs us fans of those opportunities. It's about who has the money to get on the bill.
Take the Leaves Eyes show. I don't know Eternal Embrace. However, I am familiar with SoB. The literature on LE suggests Dan&Co. would appeal to a decent cross-section of the fanbase. They've played the venue before and apparently done so quite well. In fact, they headlined the local acts for the Katatonia show so the venue knew that SoB was pretty great. So the band can't play and enrich the concert going experience of fans because its members need to eat sometime in the near future? Yeah. That really shows how much Mark's cares about the fans.