If you were faced with a choice to save the world at the expense of you and everyone you know dying, would you?

It just means you're human and honest. I wouldn't either.
Most people won't admit to that.

No. That ship has sailed. We killed our own planet.

If it was just me, maybe. But if everyone I care about is going with with me, who am I saving the planet for? Besides, I can't make that call for them. That's a choice only they can make.

People just say they would because it's a hypothetical question. Now if it were something real it would be more difficult to answer because when you think about death it's scary. The unknown.

well. if the world ends you die anyway, so why so selfish?

No, it seems more honest without pretentiousness.