I found a useful statement from a Blue on this matter:

Understand also, that while we prohibit that use that doesn't mean we are monitoring all activity to such a degree that we're checking to see if you are pressing the "2" key too quickly or at precise intervals. We are primarily looking for exploitative activity, activity that harms the overall game play environment. If you use these methods that doesn't mean that the invisible hand of Blizzard will immediately descend and smite you. You will place the account at risk though and it is possible that penalties may be applied if automation is verified.
I understand that Warden can be updated at any time to include something new that it wasn't capable of just moments after being downloaded onto your machine when you first run your game client, but as Ritley pointed out, tracking keystrokes and mouse clicks is quite a bit of data to be recording, and then expecting that someone (or AI) to be able to precisely determine whether or not someone was using software to apply auto-fire to a few of their keys is quite a stretch.

Yes, while it is certainly unethical to engage in this type of gameplay, especially when the game you're playing doesn't allow it, that doesn't mean that it's an automatic ban right out of the door.