When it's one in ten it is a public safety concern.
Why, because they are called "experimental" The kit industry is not full of crazy and unsafe designs like you seem to think. Manufactures must get FAA approval to sell a kit, and each completed kit must be signed off by a DAR to receive an airworthiness certificate, and even after that you must fly a 40hr "phase one" time alone in the aircraft before you can legally take passengers. As an A&P mechanic I can tell you that I have seen far more certified aircraft suffer from neglected or improper maintenance then experimentals.
One thing is for certain, children have no business being anywhere near something classified as 'experimental'.
Why... because the word EXPERIMENTAL scares you. There is no magic fairy dust sprinkled by the FAA gods in OK city on Cessnas or Pipers or Cirruses that make them more safe then homebuilts. Would you feel differently the same aircraft was registered in Europe or Canada so that it wasn't called "EXPERIMENTAL".
And if it is as you say that these laws are unique to the USA in the world one cannot help but wonder why that is.
They are not really, Vans and other kit companies sell kits all over the world, and they are all the same design, and all built the same. People can of course deviate from that design, but if in doing so it becomes dangerous, then said airplane would not pass an airworthiness inspection.
WAffenVW...
You really need to get this idea out of your head that one category of aircraft is more dangerous then another just because of an arbitrary name, like I already said, 90% of GA accidents are down to human factors. This one was no different, he did not follow standard maintenance procedures, and he failed to maintain control of aircraft in unpowered flight. Both human factors. Vans is not responsible to ensure that their customers are not morons. That falls under the realm of personal responsibility.
Also remember that the "experimental" category is more then just kits and home builts. Many of the classic warbirds you see are registered as experimental, just to make maintenance easier (hard to find certified parts for many of them).