Looking at single phase 230V low voltage supplies & circuits only for a moment.
In the UK, we have the ring final circuit, this is conventionally protected at 32A (old circuits will have been 30A).
We utilise single pole switching & more often than not, single pole over current protection.
Switching & over current protection must be in the line (phase)conductor, I can’t say live, as will become clear, Neutral, whilst earthed at the supply is actually a live conductor.
I will admit at this point, that I am not familiar with electrical installation practices in mainland Europe other than to say that what I have seen is often visibly poorer than the UK in many places, and I have seen many double pole over current protective devices on circuits.
Plus, the ring final circuit is a UK only deviation to EN60364.
A “standard” / “common” 13A single or twin socket outlet is normally only rated at 20A.
The “science” of the ring circuit and our old friend diversity helps to limit the current at a circuit node to <=20A.
Now in Europe, I gather sockets tend to be on 16 or 20A radial circuits, and the sockets are capable of taking this current, and are un-switched.
Combined with a double pole protective device, sockets that can handle the current, and no switching, then it is no problem.
In the event of a short circuit fault the protective device operates and disconnects both live conductors.
In the event of an overcurrent fault, the protective device opens and disconnects both live conductors.
Now you could ask how are there two live conductors when I have said the Neutral is earthed.
Well, the supply current travels down the phase conductor, through the protective devices, etc. etc. through the load (appliance etc.) and back down the neutral conductor to the source of supply.
If, you disconnect the neutral conductor from the source of supply and operate the load device connected downstream, (whatever that may be, electric heater, light, hairdryer, tumble dryer, etc.), then the disconnected load side neutral conductor will rise to supply voltage, and will be “looking” to “sink” the load current, so anyone linking this open circuit conductor and earth, will “see” full circuit voltage and as much current as the circuit protective device will allow to flow, and even for a 6A circuit breaker, the smallest in common use for domestic & commercial circuits in the UK, and not for sockets, but lighting, will allow 30A to flow for up to 5 seconds, and this is fully compliant with the safety requirements.
OK, with me so far?
Now the chances of the N being deliberately disconnected on a “live” load are minimal.
However, if you are not polarity conscious then you would inadvertently allow this scenario to arise when switching the N conductor.
So, when switching the N conductor, all live conductors are at supply voltage on the load side of the N switching point.
Hence dangerous.
Now, back to the polarity consciousness.
Now, if, the polarity is reversed in a “13A” plug, and the N is fused, in the event of an overcurrent situation, the fuse will fail, however, the phase, line, “dangerous” supply, will NOT be disconnected, so, if you have a person hanging off that relying on the fuse opening to keep them alive, then it won’t because whilst the current flowing from phase to N is interrupted, the phase voltage will still be available at the point of fault, now this voltage will still be available to drive a lethal current through the person.
Make sense?
Got to stop now, in the hotel bar & my dinner is here! ;)
HTH, please as for elaboration if you wish, I have tried to KISS this, but, not everyone will understand, and yes, I have used some “colloquial” and “common” terms, in an attempt to make it understandable.
I don’t think, I have addressed all the points in the OP, & subsequent posts, so please highlight those lacking and I’ll come back to them.
Food time!