So I haven't read through all the posts, but to me, this is actually a BAD thing. We are terrible at maintaining our environments, and this will only mean we slowly spread and wreck planet after planet like slow acting locusts (Not trying to sound like a hippy or counterculture teen, but its the truth)
So aside from interstellar travel....I don't see any practical use for this. Transmat systems maybe?
This comes down to people doing things just because they could, not thinking if they should.
Wrecking the planet is a problem. But I would say that the opportunity to do so primarily comes from lack of knowledge and ignorance. Today we know that the **** is starting to come out of the fan. But if it hadn't been for advanced technology, space technology and science, things done by people because they could, despite all those who said that they should not, we'd be completely blind. Humanity would happily overpopulate, despite diseases, cut down everything, exterminate everything, and grow rice, wheat, corn and potatoes everywhere and cause a total ecological collapse and go extinct as the last living species in an orgy of cannibalism and weird fanatic religions. All without having the slightest clue.
I had an uncle that used to say that, if God had intended us to just farm the land, we'd been given plow-bills for feet instead of a brain.
There is a distinct problem with your reasoning. How are we to know what "we should"? Who went wrong? Was it Erhu who picked up that piece of flint some hundred thousands years ago? Or was it when some plant migrated up on land, some 450 million years ago? Or was it when many single cells stuck together in a sort of colony, some 3 billion years ago? Why "should" we anything at all?
Why not accept that the mission for humanity is to spread life from Earth?
Earth is not going to hang around forever, you know. Global extinction events like collision with a large asteroid or comet, or eruption of a caldera, are not "risks". They are absolute certainties. Only question is when.
Its like hearing "They cured cancer". people are all "breakthrough in medical science yay!" but then I'd be all "Oh joy. So now we can become even more overpopulated and screw ourselves over further. Great."
Having lost three family members to cancer (No, I have not taken offense. Not at all. -Promise! I just want to explain), I do have a slightly different perspective. About a month ago I had half of my lung removed in open thorax surgery, a very uncomfortable experience, even now. (And no, I don't smoke). Now I can only wait and see. If I go ten years without any new tumor recurring, I should be in the clear.
I don't see cancer as the solution to overpopulation. It won't be able to keep up and it won't hit people before they reproduce anyway, so it mainly just reduce the experience, wisdom and knowledge of a population. The only non-disaster solution to overpopulation is developments and - above all else - good schools.