The 'it's an extra member of staff in an emergency' thing doesn't wash with me, tbh. Surely, the members of staff who're paid to be there should be able to deal with an situation and if there's not enough of them to do so, then there should be more working that train.
I don't think it's quite appreciated on this forum that railway staff are individual human beings with their own personalitiy traits. They are not homogenous and certainly not unilateral with regards to the way they interact with passengers. Some are better equipped to deal with difficult situations than others. Staff vary in knowledge, physique, street wisdom, intelligence, ability to influence and build a rapport with their passengers and so on. Some need support to deal with certain difficult situations, whilst others don't.
When I had my Govia Staff Pass, I used to pass the time by travelling on HS1 quite often. One night, on the last train of the day, the conductor was struggling to handle a case which got on at Canterbury, intent on getting to London with no means to pay. The conductor announced at Ashford that he was calling the police and that the train wouldn't move until they arrived.
Seeing as I wasn't paying and had probably used up £000s worth of travel with that pass, I promptly decided to get involved. In less than a minute, I convinced the errant passenger to get off the train. I feigned resonance and sympathy with the foolhardy passenger, something which the conductor didn't have the ability or nous to do himself. I grew up in South London, going to a school which was a breeding ground for abrasive ghetto types and having to frequent the streets where they loitered. During this time, I learnt a thing or two about the way their minds work and as such, am equipped to deal with them in any situation, whilst fortunately not turning out like them. However, many staff who aren't street wise need to to delay trains and request police assistance, as they haven't a clue on how to communicate with such people. Not necessarily their fault, but all the same, it's naive to assume that all staff are able to deal with all situations equally well.
You could say that anyone could do what I did, but I walked 5 coaches through the train the instant that I heard that the conductor was having problems. I didn't see anyone else attempt to step in. It was a bit of a sad story with that passenger, he didn't care that the police were coming as he said that he already had a criminal record and had nothing to lose. However, I said a few things to him and before long, he was on his way.
Had a couple of other situations on HS1 where the conductor was grateful of my presence and role in solving problems they weren't handling well on their own. To me, it came as second nature to help out other railwaymen, even if I didn't work for that TOC.