Threatening Presence

You're misreading the auto-cast bit. This just tells you under what conditions it'll use this ability if you have auto-cast on. In this case, it'll always keep it on IF you have auto-cast on. For other abilities, even with auto-cast on, it'll only use the ability if the "circumstances" under the auto-cast subtitle are met.

Despite the tooltip, you should not always keep this effect active. Threatening Presence is basically Growl for lock pets. If you're in a group with a tank, turn Threatening Presence off. Don't make the tank have to compete with your pet for aggro, especially since a dead pet does zero DPS.

Edit to add: In 5.0 more lock pets than just the VW have this spell. It's unlikely you'd be using a VW in a group, but the pet you are using my also have Threatening Presence.

I'm still confused about its wording.
As I can clearly see from reading it...
"Intimidates any target you attack,Increasing YOUR threat generation."

As a warlock I like to drain tank. Meaning, when I play out in the world, collecting herbs and questing, I like to let my Voidwalker be the "tank" and take the aggro while i cast curse spells and drain life. etc...

But if I read it correctly that means the Voidwalker would be doing the damage and I would receive the aggro.
Am I reading it right? Simply put, who gets the aggro, me or the Voidwalker when using this ability?