Ok, consider how tiny changes in the past 2000 years of human history could have changed stuff.
First off, if Lenin had never come to power (actually, that was part of the premise of the Resistance series)... World War I would have ended sooner because the Allies would have had Russia's help on the Eastern Front, right? So Russia is still under the rule of the Czar, and the entire cold war never happens.
Or maybe in response to Russia's not leaving WWI to go be commies, Germany's strategy would have changed so much that they could have won. So Hitler doesn't have a Kampf to write about. Nobody else writes Mein Kampf either because the Germans aren't resenting the treatment they've been getting after their defeat. World War II never happens. Operation Sea Lion, the balloon barrage, and buzz bombs never happen either. Hitler isn't frustrated with the inefficacy of buzz bombs, so he doesn't force Wernher von Braun to design the V2 for him. No race against the Nazi's to develop the atom bomb or any of that either. After the lack of World War II, the Russians, living in their home country, Germany, aren't in the cold war with us.
Either way, there's no cold war. No politicans or military strategists marketing the need to control outer space to the President of the United States. Wernher von Braun never invented the V2, and most people don't even believe the physics behind a rocket would even work, let alone be enough to get from one continent to another.
Oh, and "colonizing other planets"? Let's just say if you asked anyone, they'd think you're crazy.
Now of course I've given myself some generous points here, particularly how much of the technology developed between WWI and the Cold War went undeveloped or unresearched. But the point is none the less valid: if the way such a small span of time as the Cold War plays out (small compared to how long man has been around) can have such big effects on technology and is probably the single biggest reason anyone on earth even seriously talks about colonizing other planets, to argue that aliens from some other planet (if they even exist) are as interested in space travel as we... it's awfully self centered.
Look up "strong anthropic principle" if you ever feel like adventuring outside the box.