Humans are bad at intuiting exponents. There is roughly 200x more volume in LEO than there is between the ground and cruising altitude. Plane changes, moreover, take a lot of energy--you aren't going to get enough energy out of a collision to pollute nearby orbits.
There is no infinite space. The problem is exactly defining the number objects when that "small" amount of energy is actually enough to cause problems.
Straw man.
> problem is exactly defining the number objects when that "small" amount of energy is actually enough to cause problems
The exercise, maybe. The problem? No. In LEO, which is where Starlink orbits, there is no known solution for causing a Kessler cascade that causes more than a few billion in damage. Space isn't infinite, but it's really big.
Again, a few hundred thousand planes land every day [1]. They operate in a volume less than 1% that of LEO. To approach the object densities where we start controlling an airspace, you'd need tens of millions of objects in LEO alone. We simply do not have--not have any roadmap to having--the sort of launch capacity required to keep 30 million objects in LEO at a time.
There are real problems with more Starlinks in space. Kessler cascades are not one of them.
[1] https://www.travelandleisure.com/airlines-airports/number-of...
Space isn't infinite in the same way that 64 bit integers aren't infinite. Both are infinite for typical usecases.
Sure they can: Leading/trailing each other is quite common. Intersecting orbits are riskier, but also possible without inevitable collisions.
It is enough if it goes one round around. They can make a cascading effect which can destroy tens of satellites at once, and few fragments are enough. And closer to earth you are, less space there is. They can't all orbit on exactly the same level. There is always one which is on slightly higher level.