I personally think humans have got about as far as we can go. We're wrecking the planet. We're never short of good reasons to massacre each other. Wrong god. Wrong race. Wrong color. Wrong sex. I'm actually quite surprised a thoroughly pissed-off History hasn't waved a flaming sword and we're all back in caves in the snow, chewing on half-cooked mammoth. And even that's more than we deserve. No wonder we still can't get to Mars. I suspect the Universe is making damned sure we don't get the chance to contaminate other planets with our stupidity. It's keeping us on this one where the only thing we can damage is each other.