Because people think they can'e trust themselves because they're biased with themselves. They're self-conscious and think, "Why would anybody say that if it wasn't true?"
And...because it hurts.
We effect animals by just going about out daily lives. We plant food for the herbivores to eat, which the carnivores then eat, and then the omnivores (us) eat them. Also, pollution can affect animals...
the answer to your first question is that without nuclear fusion in the heart of stars there would only be the most basic elements like hydrogen and helium. other elements such as carbon are made...