It is, of course, not just in that thread that I have run into the same line of thinking, and everywhere we look we can observe other types of techno-optimists. They fall into several categories, although those are partly overlapping and partly nested. Perhaps a small taxonomy as I grasp it:
Transhumanists are those who believe that we will become able to improve ourselves, perhaps through genetic engineering or cyborg implants, to the point where we will transcend the human condition. Immortality of some kind and freedom from disease are obvious items on their wish-list.
Singularitarians believe that humanity will achieve a stage of technological progress after which everything will be so different that we just cannot imagine how seriously different everything will be. Why and how varies; there are those who see technological progress as accelerating exponentially and simply anticipate the singularity as some moment when that acceleration becomes unprecedentedly fast. Many others believe in
Finally, Cornucopians are quite simply those who believe that the combination of human ingenuity and, usually, the incentives provided by the free market (praise be upon it) can magically overcome any limitation or shortage that we will ever be faced with. They include people who promote that ideology quite explicitly but in a wider sense also all those who reply, when for example the unsustainable use of resources is brought up, with the naive mantra that "they" will think of something once those resources really run out. (The irony being of course that if what is meant with "they" are scientists then the scientists have long thought of something: we should stop wasting so many resources. Sadly nobody wanted to hear that answer.)
Anyway, no matter how precisely the individual techno-optimist imagines our glorious future to be brought about, the colonisation of space is perhaps the most ludicrous idea of all.
Simply put, space is huge. If you think that you can imagine even just the distance to Mars then you are fooling yourself. No, it is even further away than that, try again. No, it is even further. Much further. At any energetically realistic speed it would take even a space ship months to travel there. And Mars is really damn close to us compared to any other star system, which is the only place we could possibly find the next habitable planet. Not that those are going to be plentiful.
These massive distances combined with the hostility to life of deep space mean that we can be fairly confident no human will ever survive interstellar travel. (If anybody will even still have the resources for a space program after oil, uranium and coal have run out.)
You could try to travel very fast but there are two problems with that. First, it costs unrealistic amounts of energy, ever more unrealistic the closer you try to get to light speed. There is just no way of even storing that much energy on a space ship, and it is much less clear where it would come from, laws of thermodynamics and all that. You cannot just burn matter the size of a planet every second (which is apparently about the order of what it would take to power the Enterprise according to relevant popular science books). Second, space isn't actually empty, and if you travel really really fast then cosmic dust will hit your space ship with a lot of force, which it won't survive.
Alternatively, you could try to travel slowly. In that case, it takes thousands of years to get even to the nearest star. Now quite apart from how much time that is for cosmic radiation to kill the passengers and for micrometeorites to destroy the ship, and even assuming that somebody invents some way of keeping the passengers in stasis for so long, do you know anything ever created by humans that is still functional after, say, one thousand years? Now ask yourself if your own computer will still work after that time.
This is why I say that the whole idea is so ludicrous. We can't even build a simple house that is still usable after five hundred years without constantly being renovated but we are to believe that there will be high-tech space ships that can work that long? We can't even get our act together to deal with a few parts per million of CO2 concentrations on Earth but we are to believe that we can simply terraform distant planets? We can't even build a functional biosphere in a desert but we are supposed to believe that colony ships are possible? And we still cannot work out how to give everybody on this planet enough food, clothes, healthcare and a decent education without breaking the planet but somehow we are supposed to find the resources to build colonies in deep space? Ha.
At this point, the techno-optimist always comes with the same single argument: I cannot know what technologies may be possible in the future. Remember, people five hundred years ago would not have believed cars and cell phones to be possible either.
That may sound convincing at first sight but actually we do know a lot more than the people five hundred years ago did, and a lot of that knowledge is that certain things are impossible, such as turning lead into gold in any economic way or building a perpetuum mobile. The issues I wrote about above - how much energy a spaceship would need to fly at speeds that would significantly shorten the journey to other stars, the existence of cosmic radiation and cosmic dust, and so on - these things do not simply disappear just because we make some new invention. There are hard physical limits to what is possible, and a lot of that is already understood. Believing that they can be overcome amounts to magical thinking.
In a way, I guess Science Fiction is possibly to blame for the prevalence of this naive, overly optimistic faith in limitless progress. Yes, a forced optimism will also play its role; nobody wants to hear that growth has to stop at some point, or that we are restricted to a small ball of habitable rock in a frighteningly huge universe. But that alone would not explain the positive conviction exhibited by so many that ultimately it will be easy to achieve, you just wait, and the breathtaking self-assurance with which they hallucinate about the details of how exactly it will be done.
No, I suspect much of it is the saturation with books, movies and games showing humans travelling from star to star in a matter of days (which is clearly physically impossible) and happily living on distant planets (that in reality even if supporting life would likely have gravity, atmospheric composition, radiation and temperature hostile to humans specifically).
I like Science Fiction myself, at least the good, thought provoking stuff, especially works that explore the potential consequences of a technology or political idea. But one should not forget that it is still fiction, when all is said and done.