The current "kerfuffle" isn't just because of the pin-up girls. It's because the bickering has become so bad that it is becoming such a hassle for zuperman to host the forum and world chat that he would be better off, following his peers recommendations, and closing them altogether.
The user agreement is vague when it comes to what is appropriate or not. In the real world these definitions eat up countless hours and resources so public officials can define what is "smut" and what is art. Zup doesn't seem to want to take it on, who would?
What he sees is people's emails and reports. Lately there have apparently been many such issues that have taken zup's time and attention. Some are surely valid but there have also probably been many vindictive reports: "Yeah, just look at what they're doing over here!" It's like we're kids fussing in the back seat on a long car ride and dad has finally had enough "Don't make me come back there!"
At this point who did what is not the issue. It all just needs to stop or someone is going to get smacked.

This same thing happens when anything gets out of hand, be it disagreements that turn into insulting trash talk or complaining about people ruining games while playing within the rules.
"Dad" has had enough for a bit and doesn't want to hear any lip for a while. If we keep bickering he's going to pull the car over and we may never get to Wally World. If we can chill out the fun can get back on track.