I once read a book entitled, "Thick Face, Black Heart". In this book, the author (a Chinese woman) was talking about the virtues of being callous and ruthless when dealing with certain situations that life throws at us, and she advocated that ANYONE who wants to be effective in the living of life must develop a certain measure of Thick Face, Black Heart (callous ruthlessness). When I first read the book I was in absolute opposition to her message, but, before I got even a quarter of the way through it, I found myself compelled to agree wholeheartedly with what she was saying.
You may be wondering, "well, what does that have to do with my question?" Everything.
What you describe as psychopathy (and view as inherently bad) is really an aptitude for the virtue of ruthlessness. It is NOT an inherently bad thing, brother. Stay with me here...
I remember reading a Hadith where the Prophet (alaihi salaam) said, "Even if Fatima hint Muhammad (his own beloved daughter) came to me guilty of stealing I would cut off her hand." After the Battle of the Trench, the Prophet ordered over 700 Jews who had been plotting treachery with the Meccans killed. In 24:2 of the Qur'an Allah orders that anyone found guilty of Zina (adultery/fornication) should be publicly beaten with 100 stripes. In the middle of the ayat Allah says, "do not let compassion move you in their case."
My point in citing the above references is to say that there are instances where the proper practice of Islam requires ruthlessness, which is lack of mercy and compassion.
Not only that, a lot of vocations call for the ability to remain objective and unemotional. Generals have to knowingly send their men into the teeth of death for the sake of good strategy. If he can't make the hard (ruthless) decision to lose those men he might end up losing the war, which is the much bigger loss.
Judges also must administer justice, and that sometimes means inflicting harsh punishments on people. Law enforcement, at times of major civil unrest, will have to be willing to drop the hammer on malcontents to quell the fitnat and restore order.
You might excell at these vocations and others like them.
But, yes, we also need the capacity for love, mercy, generosity, kindness -- all of that, BECAUSE THAT'S A HUGE PART OF BEING A GOOD MUSLIM TOO. These virtues can all be cultivated. If they don't come naturally, just work at them. Just like war can turn a soft-hearted person into a cold-hearted killer, actively being kind to others can AND WILL develop within you stronger feelings of love, compassion, etc.
Dear brother! I spent much of my life fighting wars. I am a killer. But I believe in Allah and the Last Day so I do not inflict death of every person I encounter who I think needs it. I must be just. I must control the rage that sometimes threatens to break free. I must not allow that rage to control me. Likewise with you and your emotional inclinations. Control them. Allow Allah to guide you and He will make you whole in those areas of your personality where you think you are lacking. Our Lord does that.
"O' mankind! There has come to you a direction from your Lord, AND A HEALING FOR THE (DISEASES) IN YOUR HEARTS -- and, for those who believe, a Guidance and a Mercy." Qur'an 10:57
May Allah have mercy on us all, and help us turn our perceived minuses into plusses. As'salaamu alaikum akhi.