Okay so I'm just into chemistry and astronomy as a hobby because I love learning, no expert. My understanding though.

The launches definitely aren't great but they're actually not the biggest issue. The problem is the satellites, when they're deorbited, generate 50+ lbs of aluminum oxide which just floats on the upper atmosphere for years (like 30 years). Aluminum oxide is an especially potent catalyst for ozone depletion. The mega constellations that Musk wants would require multiple satellites to be deorbited daily, quickly piling up the aluminum oxide. The low orbit internet satellites are relatively short lived. So he wants either Kessler syndrome or enough aluminum oxide to eat the ozone in a year