" when in the majority of cases, the closing speed is massively lower."
Sooner or later they're going to be facing head on or near-as-dammit thanks to orbital precession mechanics on uncontrolled objects and even a "glancing blow" is catastrophic at these speeds
We've already got documented cases of the kinds of damage that can be done from shuttle days (paint flecks hitting the glass) and there used to be some footage kicking around showing how a steel 3mm nut could excavate a hole the size of a grapefruit in an aluminium block
The significance of that being that the nut is too small to track even now (back when it was published the smallest trackable objects were about 20cm)
For biologicals it looks like whipple shields help and the inflatables such as Bigelowe modules are essentially supersized versions of this, but they can only do so much and they add a lot of mass on smaller craft
It's better to try and not leave shit up there in the first place and a coordinated international cleanup effort would go a long way - this isn't going to happen whilst the most active player insists on dickwaving and trying to shut everyone else out instead of accepting that they're not the only game in town and cooperation is better than conflict