First off I have to say that this thread is not meant to bash anyone's beliefs.
Okay so the other day I was at work and for some reason had random thoughts about reincarnation. My understanding of the belief is that when you die you come back as something else. If you were good you become something better, and if you were bad you go down a step. There is also another idea of reincarnation that you just go up or down in social class but i'll talk about that later.
Anyways, the flaw I picked out is what if we killed off every other species on the planet? To be reincarnated you have to be birthed from something else, but if there is nothing other than humans you would just come back as well, a human. It wouldn't matter how bad or good you were.
As I understand, the other form of reincarnation believers see it as you are still human, but if you're bad all of your lives you will just be a poor bum for eternity, and if you're good you will come back in the higher social classes. The only way I could see this being beatable is if the world was completely communistic in the sense of money and power, and if everyone was the same race.
Please point out any flaws or mistakes I have made in my post to help better the thread.