I think you’re both missing marcosdumay‘s point. If you just want to say go to Mars then you can very quickly got far from earth and easily avoid space junk. The IIS is huge and most days has no problem with space debris. It’s only when you start talking about spending months and years in earth orbit that Kessler syndrome becomes a real concern.

Put another way, if you had 1,000 tons of mass to spread around earth orbit it would be difficult to effectively block rockets from leaving. Try to do the same thing with random orbits and it’s even less of a concern.