A 300m line holding turbulent sail kite would never have the chance getting tangled or snapping and killing someone when it whips back
Yeah there’s similar problems for the ropes that anchors are attached to as well, so they shouldn’t be using those either.
The chain for the anchor can be much heavier as it doesn’t have to be suspended by something flying in the wind when being drawn out. The water also acts as a shock absorber (as do the individual links) if the chain were to break.
What about mooring lines? They snap too.
The point is that people working on ships already know how to take precautions around lines that can break with enough force to kill a person. They establish zones on the ship that people can’t be in when the lines are being used. This is a very old problem that was solved a long time ago.