Well, it is an interesting tactic. However, you have to take a defender class to do that, AND you prevent your actual defender from marking that target. It's quite possible that will lead that target to attacking your wizard or another soft target instead of the tank. Yes, the bad guy will take damage, but he'll take that damage doing anything anyway. At later levels, the damage he takes won't be that bad either, certainly not compared to the other things you could do if you went straight warlock (or some other striker) -- you're going to miss out on having curses with your current plan, which sucks quite a bit if you plan on playing as a striker.
I am not saying this is a useless idea, but I think it is something you have to be pretty careful about.