On the one hand his point is correct, we'd have better chances of survival with two planets. But not because some aliens might arrive and zip us with their ray-guns but because we screw up the one we are living on.
On the other hand space travel is extremely costly and I cannot imagine the costs of setting up terraforming projects on Mars or travelling to a potential M class planet.
And even if we could do it I wouldn't wanna become us space gypsies who leave a place after they fu*ked it up. Locusts in space, reminds me too much of Independence Day.