I don't see why it is a dumb objection. Word choice is important, especially for journalists trying to convey information to the general public and even more so when it comes to headlines - as the majority of people won't read the article to understand the nuance.
I genuinely think a decent number of people are going to envision a situation where satellites suddenly plunging out of orbit like they would in some big budget disaster movie. You are well within your right to tell them they are thinking of the word "plummeting" incorrectly but you are fighting an uphill battle. Technical and dictionary correctness has its place but to convey information properly people must consider the vernacular.
It’s dumb because it is based on the objector imagining what an uninformed reader would imagine and thinking that anything unlike mighty Thor smiting satellites out of the sky with lightning bolts would make the word “plummet” inappropriate.
Satellites are falling relatively very fast compared to usual and some of them have or soon will burn up in atmosphere as a result, it’s a headline, not a half sentence expected to grant a degree in astrodynamics.
Likewise, why would you imagine that an uninformed reader would see the word "plummet" and understand that none of these satellites are in immediate danger of re-entry, that they will in-fact continue to stay aloft for several more months, and that in this context plummet means an orbit decaying an order of magnitude faster than expected?
You are correct, one of the meanings of plummet is a rapid descent. These satellites are rapidly descending. You are correct.
Again, though, word choice matters. Can you see where other commenters and I are coming from?
Remember that Star Trek movie trailer wherein the Enterprise (or a similar) spacecraft seemed to drop like the string had been cut? That's what I picture with "plummet".
I genuinely think a decent number of people are going to envision a situation where satellites suddenly plunging out of orbit like they would in some big budget disaster movie. You are well within your right to tell them they are thinking of the word "plummeting" incorrectly but you are fighting an uphill battle. Technical and dictionary correctness has its place but to convey information properly people must consider the vernacular.