I suspect part of the reason people have a strong response to your suggestion is that it's patently impractical, and thus easy to pick apart.

To offer one small critique: you suggest that we first need "people to migrate from Earth into orbit," THEN "take full intentional control of the planet's climate" - surely if we have the ability to fully control Earth's climate, we don't need everyone in orbit?

And, since we have to develop the technologies necessary to implement your plan anyway, wouldn't it be easier to just figure out how to remediate the biosphere directly, instead of figuring out how to get everyone into orbit, THEN figure out full planetary climate control, THEN artificially-accelerated natural productivity restoration?

Your comment doesn't add up. I need to ask more questions to triage what your positions are. Let's start with the fairly basic premise that virtually all of us agree on:

1. Current human impact on the planet is unsustainable

Now add these premises:

2. As developing world changes, our impact gets worse 3. As our own standards of living increase, our impact gets worse

Your vision of the Earth doesn't have space migration as part of our path to sustainability. Because of this, you're fighting increasing demands while at the same time needing to reduce total impact dramatically. Say that the equation is:

Impact = (number of people) x (quality of life) x (efficiency)

You can reject either (2) or (3) or both at the cost of some human harm. Most pro-tech people tend to not reject either of these, but you might be an exception. Because of that, you have 2 increasing factors, because you don't have control over the number of people are we're locked into growth for 50 years or something demographically, even with birth rates quickly falling below replacement (which they haven't yet).

There's only 1 factor left in your toolbox - efficiency. We live better but at a lower impact to the planet. Agreed, that's great, but because of (1) and (2) we already have high expectations of this factor. On top of that, we need truly dramatic total reductions in total impact. So if we need 2x improvement (which is probably underestimating) to stay level, then we need maybe 8x or 16x to get where we need to be so that the Earth is moderately healthy. That would be great, but this is magical unicorn-ish thinking. Is this what you're counting on? I want to know.

We can control Earth's climate today by Sulfur geoengineering, which I'm worried that we will not start until it's too late, and even more worried that it may not be globally coordinated which would be disastrous. This is just a band aid, we still need to virtually eliminate Carbon emissions on a time scale we're not prepared for. As long as we are here, then climate intervention will be done for us (our own selfish needs), not for the health of the biosphere.

It sounds like you agree that population levels on Earth are unsustainable and reducing them would help to preserve the environment.

Now certainly you can see why your ideas may be a little harder to accept as the scientific fact that human activity at even much smaller levels as today's population has caused terrible environmental destruction, extinction, etc., and with a lot more room to disagree, but so long as you approach the conversations humbly and with a willingness to consider differing opinions as you would have people consider your opinion I sympathize. Some people just react irrationally.

I think because it's not practical yet. I'm not sure if it ever would be, but if SpaceX gets starship right it brings us one big step closer to that. Also I think most people would prefer to remain on Earth. But moving some kinds of industry to space could be useful. Asteroids contain an abundance of elements that are difficult to extract here on Earth. If much of the demand for them was also in space due to heavy industry there, that might make it viable. Having heavy industry in space like that could really open up orbit and the solar system to us.