On the third point, space travel is actually an interesting topic. Space travel was always one of the biggest reasons for cyborgs to begin with. The term 'cyborg' first came about in the famous Clynes and Kline paper on the feasibility of cyborgs for space travel; essentially to give humans the ability to live and work in space in a nature way, as unconcerned with their basic needs and survival as they would be on earth. Basically, as a way to escape becoming a slave to the life support systems otherwise required of a spaceship. It also dramatically reduces material costs of spacecraft themselves.
Or if you go back even further, you can find the occasional cyborg as space travel solution.
HP Lovecraft's tale The Whisperer in Darkness is a great example of this, all the way in 1930, well before Von Braun even started work on rockets; and one of the earliest uses of the idea of a 'brain in a jar.' In that tale, the alien Mi-Go would surgically remove the brain of an organism, then put it in a preserving, mechanical jar. This jar would then have secondary sensory devices attached to it, allowing the inhabitant to both observe and communicate with the outside world, even in places in which their bodies could not survive. A space cyborg, before either space travel or cyborgs were common concepts. Ironically, it was played for horror.
But the overall problem with space colonization is that it is absurdly expensive because of human needs. Humans, as we are today, simply will not colonize the stars. Without adapting ourselves to other environments, and barring any near-magic technology, it would be an entirely silly proposition for the most part; you need a massive investment of resources simply to live as normal a life as you would on earth. With world population set to likely peak around mid to late century, there really wouldn't be a need to spread out for quality of living reasons. Adding cyborgs to the equation changes all that. Colonizing Mars is much easier when you can simply send down people and some supplies, without the water, oxygen, and temperature that earth-humans require. It rules out the ability to live comfortably on earth, but for a permanent colony, that should be entirely acceptable if it achieves a much higher standard of living. And that, at its core, is the biggest problem with colonization today. You become a slave to the life-support machines; unable to live as fulfilling a life as you otherwise would on earth. Until you can change that with cybernetics, we really aren't going anywhere in more than a token effort.
On the topic of human nature, that's a cop-out. It's saying that things are the way they appear to me to be, and they will thus always be like that. Entirely without justification or reasoning as to why such a sweeping assumption is the case. Most of what we are is influenced by culture; without that, we're not building technology or doing calculus, but rather scrambling through the mud for tasty grubs, seeds, and generally any other object that looks like it may be edible. Culture can make you kind to your enemies and, under the right conditioning, have you murder your friends. So to claim culture can't do things to something related to how we think is a pretty hefty claim in itself, which had better be backed up by some really substantial evidence.
But again, this is coming down to exactly what I said before: coming in with loaded terms like "extinction," to twist terms into planning a funeral for the fact that I will change slightly by the time I wake up tomorrow.