Service trains are integral to the network; steam/heritage are not.
This is wrong - 'open access' means just that. A rail-tour carrying hundreds of passengers paying, say, between £50 and £200 each is a valuable asset, and the current system of rail network access is set up to allow all permitted operators to run trains. Apart from the financial value involved, there is the unquantifiable benefit of the industry's heritage recognition and retention.
To put the entire issue into perspective, to my knowledge no-one has (yet) been killed owing to over-enthusiastic and ill-informed transgressions at stations, although a few service train drivers may have had a bit of a fleeting scare on a few occasions when they have been faced with someone close to the platform edge. Others
have been injured by trains when they have been fully observing the rules (one I am aware of personally is a man on a platform at Bradford-on-Avon whose arm was broken a few years ago by a lump of coal which bounced off the tender of a passing steam working). The risk of non-enthusiasts putting themselves in danger with steam (i.e. FS) is relatively tiny compared with some other railway safety issues - e.g. those who sit over platform edges, cross the lines, walk down the ten foot, etc. There are probably only two locos which are specifically known by the general public and which therefore could be expected to bring out the layman - 'Flying Scotsman' and 'Mallard', and the latter is not functional.
Surely the railway enthusiast 'community' can police itself and others well enough to prevent many ill-informed actions on site? I certainly advise those whom I see breaking the rules, but then I rarely go to popular spots to photograph trains and so will generally encounter far fewer incidents.
As an afterthought, I remember the seemingly huge hurdle that was overcome when BR agreed to run daylight steam again over third rail routes back in the 1990s - something that had been strongly resisted since 1968 for fear of enthusiasts trampling all over the juice rails in their attempts to secure photographs. So far, so good.