Glad you changed your mind, it really sounded like a bad idea!
Regarding empathy, maybe you shouldn't see it as a weakness. It's actually quite easy to don't have any, and I suspect most of people to not have much of it. Not caring about others' feeling or choices… Yeah, it's really common. Empathy is an effort, conscious or not.
Of course there are different levels of “difficulty”. Caring for closes one, or pretty-object-of-sexual-attraction, is so easy that almost automatic. I'm not sure the last one really counts for “empathy”: if that was the case, there would be more understanding of the concepts of “not reciprocal feelings” and “consent”.
A more tedious level is empathy for, well, anyone that don't represent an interest. Strangers, unattractive ones, people from miles away that you won't ever meet… It's easy to see those kind of people as only data, or stories. But they actually need that we try to care for them, that we make the effort to be conscious of their problems, or even opinions. We have capabilities that others have not.
And the last, most exhausting level, is empathy for your “enemies”. The ones that are different, share opposite opinions, jerks, ignorants, violents… We all instinctively think of them as just evil, or not worth it. But they actually have reasons to act as they do (not excuses, I shall emphasize that), fears, feelings… “Fighting” them efficiently means actually understanding them, and in the best case, trying not to eliminate them, but to find a solution for both of you, and maybe making them learn (or better: learning ourselves!) and become someone better.
Those two last kinds of empathy are really rare if you ask me. Because, as I said, it needs efforts. It means thinking about the group before oneself. I can't even pretend to be prefect in that aspect. But… I believe we need it.
First because I have principles. Living beings deserve to be treated with respect and understanding, no matter what they did (note: treated with respect isn't synonymous of treated kindly). But second, because that's the only way society can work. We evolve because some people chose to learn from other, and share their knowledge, opinions, possessions or even emotions. We live in families and communities because we are able to care for others. We built cities because we're more efficients in group. We had Star Wars because people listened to stories of others, and concentrated their talents to create another one!
Prisoners' dilemma, no more no less: thinking individually, the only solution is the “not worst” outcome. Thinking for the group, it leads to the better… but it's risky. The world is already in a terrible state, because human has a tendency to care only for itself. Should we be another of those, enjoying life for ourself as long as it last, or should we take the risk to make it better for everyone?
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But as I said, and as you noticed, empathy is difficult. Not only it can be counter intuitive to care for people you don't know or like, and make efforts that won't be profitable to you in the end… But it also come with a lot of dilemma, questions, fears, emotions, pain, tough experiences and even physical effects!
Yeah, I would be more “productive” if I didn't cry for lost family members, or if I didn't feel melancholia every time I think of friends I haven't seen in ages. But it is meaningless compared to all I have to gain from social interaction! Not only learning, but also gaining experiences, enlarging my field of vision, discovering other thoughts than mine, and, of course, all the joy that come from being meaningful to someone. (and Mario Kart)
So, about that girl. I don't know in what context you saw her, or how seriously it affected you (seeing you talking about “killing your humanity” with a Darth Vader method make me believe it's a big deal), so my suggestion might not be pertinent at all. But I would advice to talk to her, if you can. You might discover that she's more than just a “pretty girl”, understanding the person she is (maybe she's a NAZI omg!!!). And whether you appreciate her or not for who she is, at least you'd know her, and that could give a beginning of answers for your troubles.
And reciprocally, she would know you. Which isn't bad, really! Social interactions and empathy take efforts, and have a lot of negative side effects. But it makes you and the world progress in an amazing way. It's not a weakness, it's a challenge.
Your “superiority” is worthless if you keep it for yourself.