Starlink orbits are far too low for kessler syndrome. Atmospheric drag would clear them out in <10 years, probably much less. In fact, Starlink satellites are far too numerous for anti-satellite weapons to be effective (at least, until countries decide it's worthwhile to start mass producing orbital-class rockets to attack enemy satellite constellations, which would almost certainly lead to a loss of their own satellites as well). Russia would love to be able to take out Starlink right now, but they can't.
Nobody has enough asw weapons, and probably can't afford to build enough, quickly enough individual asw missiles, to take out even 15% of starlink. They launched four batches of 53 satellites each just in May and the month hasn't ended yet.
Additionally the US and NATO would see an act like that as barely one step below declaring nuclear war.
People with ASW don't want to use them against Starlink, they want to use them against spy satellites. Starlink would just be collateral damage.
If anyone in NATO considers blowing up satellites to be one step below killing hundreds of millions of people, I want that person fired. Because they have completely lost touch with reality, and should not be allowed anywhere near a weapon, or a job where they manage people with weapons.
Ukraine is using Starlink to control drones and Russia has tried jamming the service. Given that its not outlandish to contemplate Russia escalating. They might destroy one and say they'll do worse unless Ukraine is kicked off.
The reason taking out spy satellites is taken so seriously is it is considered a likely prelude to an attack.
Are spy satellites actually intended to detect ongoing icmb attacks? Isn't the overwhelming majority of that job done by ground and sea-based radar stations?
There is no meaningful difference between detecting a launch from Siberia, and detecting it once it's over the Bering sea. Either way, everyone on both sides will die.
I wonder how many Starlink sats one would have to take out to start a cascade to destroy the usefulness of the constellation? Of course there would be a lot of other collateral damage.