Patrick Wyatt from En Masse looked over this very thing at GDC this year, explaining how issues like gold farming, account theft and even plain old griefing affects the MMO community at large. He began looking at the other side of the equation: the people causing these problems in the first place and what motivates them. Money is the main motivator, of course, but there is no shortage of attackers who are just doing it for kicks.
So as long as you protect your own account, it doesn't affect you, right? Wyatt addressed that false assumption as well, outlining the affect of each type of attack on the general gaming community and the game in question itself. Any event that affects the game and the community at large will of course affect every member of the community. So what's to be done? Game developers never stop working to stay ahead of "the enemy", and Wyatt illustrates quite a few possible solutions.
This slideshow certainly isn't only for those in the industry. It's very informative for any MMO player, so head over to playnoevil.com and take a look at the slideshow for yourself!