It's not about space but resources, look at the world, you been around? the vast majority already lives in daily misery and it won't get better, if it continues like this we'll see some humanitarian catastrophe one rather wish not to think about.
That daily misery is still likely multiple times better than what it would have been 100 years ago. You may consider it misery compared to your own standard of living, but it's entirely possible that 100 years from now someone may consider your current situation as "misery" as well.
If you asked these people you are referring to whether they would rather continue on as they are or be put out of their "misery", I suspect we both know what the answer would be.
Additionally, I don't think it's any more useful to prioritize comfort of all living people than it is to prioritize advancement of the species as a whole. Focusing on both to greater and lesser degrees is worthwhile in my eyes, and advancing the species to the point we can get off planet and colonize other locations also vitally important in my eyes, as making everyone more comfortable (which is not the same as happier) is pointless if we're extinct in 50 years when we could have prevented that.
Agent Smith was right.
Locusts don't die out though, they just consume enough resources that they can't sustain their numbers, and their population sees a vast drop.
I would much rather humans learned how to utilize resources in a much more stable manner, bit given the option of humans as locusts that strip-mine planets or humans as a species that used to exist until they died out, I'll take the former every time. As long as we exist, so does the possibility we'll change. But I would support us doing what we need to survive as a species even if I knew we would never change.
Species survival and propagation is the name of the game. If you're (the general you) not for that, you're a fairly poor example of a human (which is not meant as an insult, it may very well be that the same things that make someone a bad human make them a good person). I would just prefer if we could achieve both, and be good people and good humans.
Again, better is relative. If you consider child mortality[1] and dying from sickness important in assessing whether people are better off or not, then those are values that negatively affect the assessment of 100 years ago.
If you consider some other values important (I'm not going to belittle you by assuming I know what you are thinking of, the only ones to that come to mind for me right now seem irrelevant), then that would affect the assessment of 100 years ago positively.
Personally, I think there are far more indicators, and far more important indicators, that affect the assessment of 100 years ago negatively.
Birth rates are high because of poverty, not the other way around. You need a lot of kids if you want your family to survive harsh conditions. Eliminate poverty and you'll see birth rates go down to a sustainable 2-per-family.