Everybody wants something for nothing. In the case of online games they want titles, power, and prestige that can be bought with trivial tasks repeated over and over so they use bots. I have never used a bot and never intend to do so but I think a lot of the anger and vitriol directed at them is very misplaced. Tobold talked about how bots show that gameplay is awful because people wouldn't bot if they actually liked playing the game. This is clearly mistaken because I know people who loved playing WOW but who botted to generate extra cash. When they were home they were playing WOW, when they were away their bots were killing stuff and making them money (badly). All the bots proved was that it was easy to perform some kind of activity that generated advantage and people wanted that advantage. The only way to stop bots is to make any possible gameplay that generates advantage so difficult that a bot cannot be written that could perform it. Yeah, try ever getting a casual player to play *that* game.
Occasionally I cruise over to the D3 forums and there are always strident complaints about bots. While I agree that bots do change the D3 economy I am not at all convinced that they actually make things worse in most cases. For a solo player of course they have no impact. For a player who goes into open group games and has bots clogging up their game doing nothing the bot is obviously a problem. The tricky question is what exactly do bots do to the Auction House? I think the answer is that they make nearly everybody much more powerful but concentrate that power in the hands of the botters. They grind up enormous numbers of drops and because each character only needs 1 set of gear all of the extra gear ends up on the AH. The botter claims the best of the best, of course, but the quality of the gear on the AH rises significantly and everybody can take advantage of that. Bots make all characters more powerful and unless you are primarily worried about how powerful you are vs. the top players it is nothing but beneficial.
Really there are just two downsides to bots that end up being significant. First off they use server resources, which can be very frustrating for people who want to log in and cannot or who have to deal with low performance. This raises the cost for games so everybody suffers to a small extent. The other downside is the perception of unfairness. People get angry when others cheat even if the cheating is very minor. I know I have an irrational hatred towards botters that far eclipses the actual negative effects they have had on me, which are surely near zero. Perception is important and if a company could actually get rid of bots entirely it would be really good for their press - good luck with that though.
We need to accept that in highly competitive environments people will dope up (Hey Lance, how's it going?), use bots, or resort to other nefarious schemes to win. Not that we should stop fighting the good fight but frothing rage isn't going to fix these sorts of problems now or ever.