Bots damage more then we think they do.
But mostly bots bring a lot of gold in the game that shouldn't be there, which causing the gold inflation a lot. Gold is getting less value day by day. Same story to those chinese gold farmers. I'm certainly sure about the fact that half of the gold wouldn't be there if the game didn't have any botters and chinese gold farmers. That armorpiece you bought with 9.000 gold yesterday? Im sure it's price wasn't even the half of that if there weren't any botters. That new Grand Expedition Yak mount? I'm sure it's value wasn't 125.000 gold if there weren't any bots in the game.
If Blizzard didn't care about botters, i see easily that all values were doubled from the values we use nowadays.
So yes, we should care about botters.