Time Travel is so Legit

So you know how, in like every time travel book/movie ever, they go back and mess things up? Like in Time Travelers Never Die, and, well... there's a lot more you can probably think of.  But they always mess up the past, so what if future people on Earth messed up the past, and we are living in the messed up future? like in Dragon Ball Z, when there's one future where everyone on the planet just dies, and one where Goku lives and saves everyone?  Well, I think we should be a lot more careful, because we could be the poor civilians who have to just sit back and wait for the androids to come and slaughter us all.  I know there is not much point to saying this... but, it is kind of a relief to think that we could just blame all our problems on people in the future.  Which we really shouldn't... but still, how about it?