Do humans need to find another habitable planet?

One of the major aims of deep space exploration seems to be finding a planet that is habitable and humans can live on it. I'm wondering if there's any 'need' to do that. Of course, the first counter argument is this "What if we find out that the life on Earth is about to get destroyed? What would humans do then?".

I really wonder if that's happening and whether we really need to find another habitable planet. For once, most of our sophisticated telescopes have told us that we're safe from a big object hitting us or our solar system getting gulped by a black hole.

But even if we make other planet habitable; what are we going to do differently on it? That makes me wonder, what's the ultimate goal of human race? If there's any, at all.