THUD is for cheaters! It's not gamebreaking like botting, but it's certainly not legit. My problem with THUD is that it removes a large part of the "skill" difference between players. With THUD u don't have to think or actually be good at the game to be effecient, you just have to look at some numbers calculated for you by the program and spam some buttons... and honestly, how fun is that? Being a faceroller for a cheat for a video game... pathetic if you ask me.
The issue is that THUD makes D3 less rewarding for skilled players and the most fun games are the ones where skill and dedication mean alot, which it does in diablo, unless you cheat. It's not HEALTHY for the game, bottom line. I mean the entire point of diablo is that it takes time, dedication and creativity to actually be good, which is also why its rated mature. So dont cheat, if you cant handle the math go play Skyrim or something.