I think being created by an evil wizard with knowledge in black arts with dna from a race of nomad gutmunching mutant savages leaves nothing of good inside her,she's a crazy efffffing bitch.

I don't think they are evil, they are just dumb.

Baraka is the only Tarkatan who was shown to be smart in the old timeline and he is the only one in MK9 who seems to talk(out of the all the other Tarkata) and has a brain, it is also shown in his MK9 ending where he kills Shang Tsung who morphed into Shao Kahn.

Now to answer your question, the Tarkata are usually unintelligent and bloodthirsty, which in terms would mean they are evil since they are driven by their love to kill.

Mileena on the other hand, doesn't have the same problem, she is more like Baraka, she is smart and wasn't really shown to be a character that is solely motivated by killing.

however, I think she admires Shao Kahn and wants to be like him, meaning she will always want to stay evil and rule.

So I think being half Tarkatan does make her a bit evil but it isn't what truly makes her evil, if that makes sense.

I'm guessing the MKX plot will at least touch on her motivations if not explore them a little deeper. She's got a mean streak though. Tarkatan blood + dark sorcery + cheating ass Reiko = one angry deposed Queen.

Well, in her MKX Amazon Bio they said she was made to be loyal to Shao Kahn because he thought Kitana might betray him.