It will happen in one shape or form regardless of the inane limitations put on the players at the end of the day.
Solutions
1. If they are in your party kick them
2. Ignore them becuase they are not effecting your gameplay in any way and there is nothing in the ToS that sais you can't /autofollow a person and have them fight for you.
Happens in everygame, it clearly shows at the end of the day who leveled without playing there job and who did. Hell it happened in XI all the time. "Level me guys I'm bringing my PL to cast cure V every 2 minutes! Lulz" and people ate it up. bringing in arbitrary limitations to the normal user is just punishing us in the end.