The other end of the argument is also interesting. It is possible that this has already happened before the age of Homo Sapiens, and we lack the one crucial thi

The other end of the argument is also interesting. It is possible that this has already happened before the age of Homo Sapiens, and we lack the one crucial thing that makes fusion power possible, say, deuterium oxide (heavy water) in sufficient quantities. It’s a ‘you don’t know what you don’t know’ situation — we could be living on a stellar neighbourhood that is already tapped out of that crucial resource, forever doomed to travel the slow way, never able to go more than knee deep into the vast ocean beside us.