but have you ever thought what might happen if even a tiny bit of incoming debris, natural or man made, impacted your thin aluminium tube at altitude?
Not really as the odds are spectacularly low. Like really really low. The odds of impacting incoming debris in the collective shape of another aircraft is orders of magnitude larger. Only one person has been hit by a meteorite as it came through her roof as she lay in bed - although I think a dog was killed by one back in the 50's.
Most meteoroids (and space junk) burn up by the time they get anywhere near the stratosphere. On the Space Station, however, 430km up they have installed shields to protect against the very real risk of depressurisation due to meteoroid impact.