I'm having trouble seeing your argument for all the straw people. I don't care what you believe, I watched her walk down my steps one step at a time, both feet stable on that step before taking the next one. Why? Because her whole life she's hearing "NO! BE CAREFUL! STEPS ARE DANGEROUS!" so of course she's terrified and has no confidence that she can do it.
>meanwhile other anti-helicoptering activists argue that breaking bones is a necessary part of healthy development
Who says that? The fact is, the broken bones came, in her case, from the fact that she has no experience or confidence in things kids her age are able to do but ends up playing with other children (often younger!) who can. My kids already had their falls and scrapes when they were younger and closer to the ground. Now they know how to swing on a swing, roller blade, etc., without getting terrified and falling over. They also know better how to fall to minimize damage because they have experience with it.
Look, over-protection is simply bad [1]. That's why it's called over-protection. If you're doing it, you're harming your children and you need to stop.
[1] http://www.brainy-child.com/articles/negative-consequences-h...