>Do you believe nobody at SpaceX, or their direct competitors, has thought about it?

It doesn't matter if they've thought about it. You can think all you want about something but ole Private Murphy operates in the real world not on paper when he sets about mucking stuff up. They're talking about launching 11,925 satellites. That's nearly 10 times the current number of orbiting satellites.

This is not a rational fear. There are at any time an average of 10,000 planes in the sky, carrying 1m+ passengers. These 12,000 satellites will each have more space available and very regular trajectories, without ever converging on major nodes.

One should note that your opening statement is that "It doesn't matter if they've thought about it." This is not how innovation, manufacturing, maintenance, and risk management work.

>This is not a rational fear. There are at any time an average of 10,000 planes in the sky

Planes don't have flecks of paint, screws, etc flying by them at 28,000 kilometers per hour with the ability for one impact to send debris going dozens of directions.