> Even if everybody eats twice as many animals as they do now and moves further away from their workplaces, Earth will remain a more livable place than Titan. Maybe that isn't true if we kick off a nuclear war, but it probably still is.

Sure, but colonizing Titan will ensure that we develop the technologies we need to sustain the species under those conditions, rather than having to "do it live" when a nuclear war / asteroid impact / what have you happens.