I understand the allure of separating heavy industry from people and parks and nice things, to centralize the pollution. But if you put heavy industry in space and most people still live on the ground, it takes an incredible amount of energy to get the raw resources into orbit and bring the finish products back down. If you mine the moon or asteroids, that still takes a lot of energy to get to space-based factories. If you put the factories on the moon or near the asteroids, that's still a lot of energy to ship finished products back to earth or orbital habitats. If you put the factories on Earth near the resources, it's a lot of energy to get the finished products up to orbit.
Besides, factories pollute a lot less now than they used, they are getting cleaner all the time, and we rely on heavy industry, percentage-wise, a lot less than we used to, and all these trends are going to continue.
And if energy becomes so cheap (fusion, cold fusion, who knows) that all this shuffling is practical, then it would also be practical to simply pour all that energy into making heavy industry even cleaner. The problem with cutting pollution isn't the idea, it's doing so efficiently, and with cheap energy, efficiency becomes more relative.
So what am I missing? What is the actual benefit to separating heavy industry and people?