interesting debate this. The fight against the apparent common sense perception (to wear a lid is best) could be more to do with not wanting to be told what to do or being an seen as an individual. I hate being told what to do and would probably rebel against any law forcing me cover my noggin with a bit of way over priced plastic and polystyrene.
However as I’m a coward and don’t like pain:
1, 4
2, lots
3, not sure but can see it could have happened
4, 0.1% when doing a post fettle test. this being one of the times I could hurt myself due to mind set of low risk. Bit like tow path rides (oops).