I'm taking the parts of this write-up I don't have expertise with a grain of salt after seeig this.
Kessler cascades are real. Particularly at high altitudes. They're less of a problem in LEO. And in no case can they "[cripple] our access to space." (At current technology levels. To cripple access to space you need to vaporise material fractions of the Earth's crust into orbit.)