> Why are so many people just desperate to imagine environmental, economic, or social harm from any new technology or ambitious projects?

Rockets aren't new technology and they are not imagining the environmental harm. It has been known for a long time. It is just that with only ~300 launches per year (and about 35000 launches ever) the harm has not risen to the level of something that has to be limited.

A million data center satellites is a significant increase in that harm. Furthermore data center satellite are expected to have a service life of maybe 3-5 years so there will be an ongoing 200-370k replacements needing to be launched. That's 3.3-6.2k launches per year at 60 satellites per launch.