There are several causes as to why the 'voices in your head' are angry, discontent, and outright cruel. A lot of it has to do with your current living situation. If you are able to help illuminate my understanding of your living situation, I will be able to offer much more in-depth assistance.
First things first; the voices in your head are literally your own creations. Now this may seem incomprehensible at first, and that is ok. What is important is that you understand that they are your creations, and that they will answer to your bidding. This includes diminishing should you will it so. They develop out of instances where you have judged yourself as unworthy, or where you feel you have made error in some way. When you make these judgements about yourself, your mind will create an echo of this, and repeat it until you change your understanding of the situation that this feeling arose from in the first place. Each one can then, essentially, be identified as a marker, showing you where to go in your mind in order for you to be able to apply the necessary changes.
The voices will change over time to be more noticeable, and because of this they will often resort to more oppressive language. This means they will change what they were originally saying into something different in order to keep your attention, however will either maintain or amplify the negative feeling that they were echoing. Because of this, it is important to ask yourself 'Why do I feel this way?' In time, with patience, you will know. It will either come to you through intuition or by the presence of a new voice in your head. Asking for guidance or help during this will also help you to find the answer. When I say asking for guidance, I mean ask yourself for guidance. While this may not seem to make any sense at first, you will understand how this works only by doing this for yourself. Allow yourself to delve the depths of your own mind. The voices in your head will start responding to your questions, and the original location of the 'injury' will be revealed. Simply trust in yourself. While this may take time, and will take patience, the effort alone will begin to change how the voices in your head talk to you.
The second thing I feel that should be mentioned is this; Understand that with death, you are only going to have to repeat those life lessons that have caused you pain through another life experience. This is a very inefficient and self damaging way of attempting to fix these issues, because on top of having to relive through these lessons until you learn what they have been brought to you to teach you, you will have to repair past karma that was not corrected before you parted. I encourage you to use the life you currently have to revisit these places, these lessons while you have already received them. This can be done in the mind simply by thinking of them. And the voices in your head, the ones that are telling you to do self harm, they can show you where to go.
Understanding this is important in being able to take your mind back, and this is what we are going to do, one step at a time.
I want you to know that all of the power is within you, being forgotten. All you have to do in order to retrieve it, is to accept it. Never be doubtful of yourself, no matter what it is that you have been taught or have taught yourself. You are not a 'pussy' when you choose life over death. This shows you are still strong. Your strength will not wane unless you yourself choose for it to. Nothing has control over this but yourself. Do not fear the reclamation of your strength. This is your liberation. And you ARE free, all you have to do is claim it. Claim your freedom.