Biggest tabletop system pet peeves

[Max_Killjoy]

Conflating ideas again. IME, the type of personality likely to create such a setting is the type of personality likely to railroad. They aren't a jerk and railroading because they create closed worlds, they create closed worlds, and they railroad, because they're a jerk. That's the casual direction.

Again, purely your experience.

The vast majority of gamers have not reported running across the problem, with one exception -- the aforementioned assumptions by certain players of universal applicability of all published material to all gaming tables, such that they take offense when a GM tells them that no, they can't bring in their level 12 snowflake with multiple PrCs from wildly divergent incompatible settings who is "half" five different races and blessed by Fate and blah blah blah blah blah.

IME, most people consider the Forgotten Realms to be a different setting than Ravenloft or Krynn. Darn overused words.

If characters and information can travel between them, then they are not isolated settings. Perhaps subsettings, or settings part of an "oversetting".