How do you define "enthusiast"? It's someone who is enthusiastic and the new, unaware, fascinated enthusiast who knows no better or lets their enthusiasm overtake their adherence to rules or consideration for their and others safety.
It's within this wider extension from your responsible 'rail enthusiast' to the over enthusiastic that the issues of trespass and safety lie - but unless they can be separated, there's every chance the few will bring the controls needed for their own safety on the few onto the many.
Exactly - in the same way that the vast majority of decent, well behaved soccer fans were impacted by the actions of a relatively small number of high profile hooligans.