Informing an authority figure that someone is breaking the rules is not being a vigilante. A vigilante in this case would be if I had charged them a penalty fare or removed them from the train. By your definition, anyone who informs any authority about any crime/rule breaking is a vigilante.
"Help! I'm being mugged! Call the police!"
"Can't mate. That'd make me a vigilante."
That is also rubbish. Your statement means that if I call 999 and say "my neighbour's house is being burgled, please send the police" the response would be "go away, stop telling us how to do our jobs". I am giving information to authorities which they may find useful and may wish to act upon.
As a more general comment, I expected a level of "don't bother to get involved" (which is fair enough even though I don't agree with it) but "vigilante", "get teeth knocked out" and school playground arguments? Really?
Sorry, but your comparison with calling the police to a mugging or burglary doesn't work at all. A completely different situation.
You should wonder why someone potentially fare dodging next to you would let you know that rather than keeping schtum. There's a high chance they're trying to annoy or intimidate you.
I didn't see the teeth knocked out post, but multiple people have quoted the "snitches get stitches" adage. I'm not defending that philosophy, but an awful lot of people live by it.
There's nothing "school playground" about pointing these things out. Running to a guard to say "I think those people might be naughty" could be seen as pretty child-like though.
I've mentioned it before on here that I know (an acquaintance, we both know who each other are) who is currently serving a 10 year prison sentence for leaving someone with brain damage after an argument on a train.
I declined to sign a petition complaining about the length of his sentence, with a lie about my job (very very loosely connected to the jjudiciary at the time) preventing me from doing so, rather than saying I agreed with it. Sometimes being forthright isn't the right approach.
I stand by using the word vigilante and hoping people do "mind their own business".