And: What are the externalities of this? The current 10700 satellites are expected to have a lifespan of about five years. So, averaging these burning up in the upper atmosphere there will be one deorbit ever four hour.

If I were to ask my relevant government regulator if I were allowed to burn the equivalent of a few electric cars every day without capturing/scrubbing the pollution they would laugh me out of the room.

But ”in space” nobody can hold you accountable, so burning an order of magnitude more like this is somehow on the table.

SpaceX has spent under $30 billion for Starlink.

That's less than maintenance opex for mobile networks operators in the US alone.