Aaah, but you see, herin lies the problem.
There is no set future. At its simplest I guess you can look at it this way: If time is a line we travel along and there are things that exist on that line, and there are events that happen on that line. Then that's fine. But the moment you travel back, the future does not exist. Just by being present, you displace particles that would in your future be elsewhere. That presence in itself is proof that the future you come from is not the same future as the one that lies ahead of you. In the moment, there is no timemachine, there is no future you, there is only the present and your existence in it. If you shoot your father, preventing you from being born, all you do is change the present. Because as I said, the future does not exist. The future you doesn't go back in time, the present you however has already done so. After all, time is just our observation of the processes that happen in space. The past exists only as an illusion, what we observe is the information that lives on in the particles that have interacted.
So I say again, if you have a piece of matter, and you send it back in time, then you have two. Does that not violate our current laws of the universe?
Please correct me if this makes no sence, I'm up way past my bedtime...