NEITHER YES NOR NO, BUT - FIND OUT AND STUDY
I think - neither yes nor no. But rather - wait. Any terraforming project will take thousands of years. And - they talk sometimes as if we must start it right away, next decade.
RISK OF LOSING TECHNOLOGY IS A CLEAR SIGN WE ARE NOT READY TO TERRAFORM
But there is no urgency. If you are worried that we will lose our technology and space faring capabilities -well - that's a clear sign we are not ready to terraform. Because - it requires a stable peaceful technological civilization with the capability to start a 1000 year long project and bring it all the way to completion.
If we are likely to lose our technology some time this century, we most definitely should not terraform. Because how can we possibly hope to keep up a high technology project for over 1000 years?
ASTEROID IMPACTS NOT A PROBLEM
And as for asteroid impacts - that is just not a problem. There's no chance at all of total human extinction causing impacts for several hundred million years, and only a tiny 0.0001% chance of a Dinosaur extinction type impact by end of this century - but we aren't dinosaurs, we have technology and apart from anything else would have some humans for instance deep underground in caves or in submarines - or whatever - many ways to escape it far easier than traveling into space.
TAKE OUR TIME, MORE HASTE LESS SPEED
So, don't rush! Take our time. There may be things we can find out in the next century that will speed it up so it only takes 500 years instead of 1000. Or may be things we learn that lead us to say "Thank goodness those people in the C2100 did not terraform Mars / Moon / whatever it is" - because they just see Mars and the Moon differently from the way we do now.
WHAT WOULD THE PEOPLE IN 3100 WANT US TO DO?
If we terraform, we are not doing it for ourselves. We won't live to see even the first stages of it completed, nor our children. It's for 30 generations from now, or possibly more, several hundred, even thousands of generations into the future depending on how far it goes and how long it takes.
I think only a remote chance that the people in 3100, a thousand years from now, looking at whatever remains of some 21st century attempt at terraforming Mars or the Moon will look and say
"Aren't we lucky that the started on terraforming so soon - they had such a far sighted clear idea of how to do it, well in advance of their time".
You might hope they would see it like that - perhaps - but I think that's unlikely.
Far more likely to say
"What idiots they were, way back in the 21st century. to think they knew how to terraform planets. If only we could go back in time and stop them.
If only we had the opportunity to study and then work with their pristine solar system with our advanced technology, how much we could do!".
And the thing is - that terraforming planets is as you say irreversible. Once you add a new reproducing lifeform to a planet that wasn't there before, especially a resistant microbial lifeform - you can't, realistically, remove it again.
EXPLORE IDEAS INSTEAD - AND SMALLER SCALE EXPERIMENTS
So, I say - no we shouldn't, not yet. But should explore the ideas, we can learn a lot about thinking through ideas for terraforming planets.
If ambitious we can take it one step further and carry out experiments in closed system habitats. And eventually big closed systems like Stanford Torus habitats.
Meanwhile also study exoplanets.
All that would cost far far less than a terraforming attempt - and we would also learn a lot more from it, in controlled conditions so we know what is going on and why things went wrong.
And if we are really lucky -maybe we will contact ETs, likely to have had technology for millions, possibly billions of years already, who have prior experience of terraforming their planets - and can advise us about what went wrong, and what went right.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
4.8m answer views110.4k this month
Top Writer2017, 2016, and 2015
Published WriterHuffPost, Slate, and 4 moreHuffPost, Slate, Forbes, Newsweek, Business Insider, and Science 2.0