iMHO, we need to address first the problems on our own planet to ensure that it remains habital. Waisting resources on going to other planets is unfortunate. I do not buy the argument about spillover of the science involved is a justifiable by-product. In a word, it is just hubris.
I apologize ahead of time, but in my opinion I find this attitude dangerous and naïve. It is dangerous because it does not look at the big picture in a long term way. It is naïve in that the person having it has usually got a fantasy of everyone getting along, working together, and doing things right will become obvious to everyone.
Now that I've been rude - sorry - let me try to explain myself.
Should the Earth be preserved and all of us should solve all the problems here? Of course.
Will we? We sure haven't managed to do it so far.
Have we solved some problems? Sure. But not very many and we are creating more than we are solving. The human race can't agree on hardly anything.
Will the human race come together under threat? Maybe. We're under threat from global warming and there are plenty of people that could care less and there are plenty that say there isn't a problem at all. You can't control stupid people doing stupid things.
To get people to work together you would have to force it to happen. That would take away their rights and their freedoms.
Where are a lot of the problems with the environment and resources coming from? 7 billion people on one tiny (and getting tinier) little planet with limited resources.
Limited space and limited resources means that something, someone, or even a natural disaster could devastate the limited space.
Out there? An infinite amount of space. An infinite amount of resources.
We have to get out there, and as soon as possible. Anything less can mean disaster.
I kind of like us human beings. We are the one and only sentient being we are aware of. It's a big Universe out there. It's time to grow up and get moving.