Typically the place to worry about space junk is in Geostationary orbit. It's a tight band with a lot of satellites trying to use the same space. Also is it is about 0.120 light seconds away introducing 240ms of packet latency. This makes for slow internet communications. However a lot of broadcast satellites are found in GSO in addition to GPS satellites. These orbits are tightly regulated by government organizations.

The innovation behind Starlink is the satellites are disposable so you can stick them in very low orbits and not be too hurt by them de-orbiting when they run out of fuel for stationkeeping. In addition they keep a reserver to intentionally de-orbit at the end of their lifetime. This eliminates the danger of Kessler syndrome because the thin atmosphere slowly drags everything down even if the satellites are rendered non-operable. In addition you have insanely low latency at 440 km (Only about 2.8 ms) which is faster than fiber lines because they don't have to worry about re-transmission every 2 km. Satellites at 440km can maintain communications using line of sight laser links up to a theoretical 5400 km. (Although usually it's only going to be under 1000km)

The first Starlink constellation tested this with a few sacrificial satellites deorbiting themselves

Yea, they are in super low LEO and designed to de-orbit pretty quickly if not station kept.