This has to be the silliest DLC controversy yet. Someone wants to pay money to easily trigger an animation that has absolutely no effect on gameplay? Fine by me. It's not like the fatalities are all that hard, and even if they were, they don't have any gameplay effect beyond a cosmetic one.
You could argue that it's not in keeping with the legacy of Mortal Kombat. You'd be right, but honestly...who cares?
There are plenty of shady DLC practices out there that are worth grabbing your pitchforks and going after developers. This one...well, this one isn't one of those. This is just a stupid DLC idea that no one with any sense is going to buy. It can be safely ignored.