[berntb]

If the Orion project in the 1960s hadn't been stopped, we might have viable interplanetary colonies already. Also, if NASA hadn't poured most money into the shuttle (and hence had a reason to kill competing projects, for job security) the space exploration/colonization would be much further along.

Even now, we might be less than 50 years from independent colonies, if lower costs for space launch finally "take off" with Musk.

This implies that if there is some common reason (e.g. a physics experiment with unexpected outcome) that exterminates budding civilizations, it ought to have already happened (and we were lucky) -- or it is something big enough to blast a whole solar system.

Edit: It would be interesting with percentage chance evaluation of the possibility that the Shuttle project doomed humanity to extinction...?