No, they do not get stronger. The key to doing launches consistently is to keep the length and angle the same. Since the "ball" here is a ragdoll, even very slight changes can have some drastic effects.
The launch force is linearly based on the length of the line and I balanced the "normal" forces to be what ever looked like the most natural to me. Obviously this enables some ridiculously high forces when going for the max distance. The higher forces do have their uses too even if they will kill on contact with anything. Somehow limiting the launch force to disallow higher forces would be stupid, think of a golf game where the power meter was the exact thing for a hole in one.
Also, destruction is fun (to me at least)! Extra deaths aren't really punished at all, the stars are pretty much only there for bragging rights. One will most likely easily earn 2/3 stars by accident to be able to skip even a third of the levels if needed.
Thanks for playing!