I bet that a safety inspector can tell you all about the risks of leaning out of windows to wave your arm and shout: the door might fly open, you don't know what's coming around a corner... etc....
Well, as for shouting I quite deliberately hadn't referred to the whole bellowing thing, which is really little more than the sort of loutish behaviour that you get when lots of blokes get together and get drunk in any situation, and not hard to work out its origins. I am interested in the origins of the specific phrase "My Lordz" however.
In the specific case mentioned of pulling into Darlington from the south, everyone can see for several coach lengths ahead what's coming (a long, open platform). Most flailing occurred as trains were departing from or arriving at stations, where the speeds were low and obstacles predictable. You have to stick your arm out a hell of a long way to meet any obstacle anyway (except perhaps vegetation), so unless you're Mr Tickle you should be fine.
As for doors flying open, how often does this REALLY happen outside the most fevered fantasies of a foaming-at-the-mouth health and safety obsessive?
Statistically, the number of flailing-related incidents is probably quite small, but H&S is very much a what-if sort of regime, and one way of minimising the risk is to prevent flailing. I'd hate to see MK1 stock, such as the Lymington 421 units or Chiltern 121 banned. I'd rather give up flailing if it means that heritage trains are allowed to keep running in mainline service.
I'd also rather give up flailing than lose Mk Is etc (irrelevant really because as a sensible adult I haven't flailed for more than 20 years, but this doesn't mean I disapprove of it), but this is about more than just flailing. It's about the idea that people should give up something almost completely harmless just in case someone in an unearned and unwarranted position of power should irrationally and without warning decree that it's undesirable in some way. We are being scared into believing that things that rationally we know to be either safe or to carry a minimal and acceptable level of risk, are dangerous.