If I put citations into everything I write, I'd be a Wikipedia article, and people would still criticise the conclusions without reading any of them.

But contrawise, I do have data, they're broadly categorised as "history", "biology", and "all the stuff cited by Stuart Armstrong that time".

I think its the fact that if we really wanted to, we could probably make it happen already today. On a scale of a couple hundred million years, its possible we could reach most of our own galaxy, which is a small slice of time in the life span of the Milky Way. So the question remains, why hasn't this already happened, or has it?