Are there that many passengers around who don't understand the reasons for a door and struggle to workout if to use it or not?
The emergency egress capability is not theirs to use at will except in an emergency, (which the OP's description of the event doesn't describe it as one).
You saying once the platform side door has opened by one the other passengers are going to start jumping off the non-platform door.
The discussion is about a situation where no doors were open to allow passengers to alight.
I've never seen anyone trying to exit a closed door accidently while the others open.
Where was it said that somebody tried to exit a closed door "accidentally"?
Even if the passenger did (in an extremely unlikely chance) accidently open the wrong side they would still notice its not at a platform and head over to the other side, passengers do open doors themselves even down south, they can see when trains at a platform and can still pull a handle at any time while on the train without hearing off train staff.
As
@Deepgreen said in post #44,
"Not always - I remember at least three incidents of wrong-side opening, including one at New Malden on a SUB where someone got up from a nap and opened on the wrong side... ", so your
"extremely unlikely chance" situations do occur, and injuries or even death is 'quite likely' if it gets that far.
Its complete nonsense to suggest that it's not safe to trust passengers to judge when to pull a handle themselves even with an announcement when the option to use it is there every minute they're on a train.
It definitely isn't safe to trust passengers to freely judge when to pull a handle that is expressley there for emergencies. If the culture of the egress facility being a convenience for the impatient passenger then that would allow a hazardous action regressing to normal, - a very dangerous situation.
If there is that mistrust in passengers making their own judgment why on earth do trains have so many chances to do so.
Because almost every passenger trusts the that railway is charged with their safe carriage, and disobeying very prominent notices prohibiting certain activites is the territory of arrogant self-interested fools.
As far as why the railway has so many areas of operation where hazards do exist, - well, the UK railway is almost 200 years old and attitudes of danger and responsibility were ignorant of the dangers created by the new railway, and there was little if any legal recompense if an innocent assumption of a lay traveller resulted in harm to themselves or others. Luickily, in the UK, every significant incident on the railway is independently investigated and where possibl, preventative measures embedded in law to preven or at leat mitigate similar events in the future, - thus in the railway, we have a transport system that has a very low level of inurues and deaths.
We live in a (legally) much more caring society now and everbody has a legal obligation to maintain the safety of others in their actions. This is how the railway's grandfather rights are tolerated where practical, to this day. There of course quite a few individuals who presume that it doesn't include themselves and their superior knowledge of 'things'* allows them to ignore warnings intended to protect eveybody including themselves.
* RUK seems to have a few members with some railway knowledge and who think that safety is just
'stuff and nonsense' as this and other threads seems to be revealing.