We'll take important steps to ensure the continuity of our species by making it multi-planetary. The risks are diverse and well known such as climate change, thermonuclear war, geomagnetic reversal, asteroid impacts, etc. Some of these are within our power to change, but others -- such as the asteroid impact -- are more easily mitigated by colonizing two worlds (than overcoming not just the politics but the physics problem here on Earth).
The continuity argument is a strong one, but it is weakened - in my mind - by assuming sufficient time to colonize anywhere else, while trying to survive on our current lifeboat. I don't doubt the intent, but I think the timelines do not match, in that we will exhaust resources here (both fundamental and good-will) way before any second colony becomes viable.
