My first thought is I am glad I chose FFXI and not some of those other games....
I think we have some people out to take advantage of others. Many of their stories have been posted here, mostly people taking gil or items from others on some pretense and then logging off. I personally had this happen on a BCNM where a player suddenly QMed themselves at the end of the fight and then quickly logged after grabbing the loot. (I might add this situation was eventually successfully resolved through contacting GMs). Another is the prank where people lead a new person to Jeuno or Selbina when they are very low level using sneak/invis, again on some odd pretense, tricking them to resetting HP, and abandoning them there. I have heard of that, and that's a pretty mean thing to do to someone just trying to find their way in our world.
However, without the PvP elements that exist in some of the other games, I don't know that we have as much of a problem with this as other gaming worlds. Sad to think about people who play these games solely to hurt others tho. /sigh