To have a group for "erotica only" would take 2-3 people minimum to make the group successful . It would take time and dedication not to mention a well thought out format or objective.
There would have to be rules in this game
It wouldn't make much sense to provide a group just to post erotic material, there is a thread for that
Which means there would need to be something to entice the writers like critique
I believe Groups have full editing options which means lovely little miss sexy avatar may choose to post nudes to go with her post. Art is acceptable? So where do you draw the line with "art"?
This would be a huge task with someone willing to do the oversight it would be unfair to throw it all to the wind and leave Web Miss or Mods to supervise
It's an idea with alot of responsibility.