Regardless of what we think of MerseyRail for what they do and don't enforce, good on them for pursuing this. If this was enforced more widely (and more cases were then made public) then it might help to make it even more anti-social than it is, and should reduce the occurrences.
See it regularly on both trains and buses, but rarely say anything unless I'm about to alight off and its clear that the perpetrator isn't.
Different scenario, as safety is involved as well, but high profile campaigns have over the years increased the anti-socialness of "car offences" such as wearing seatbelts or drink driving, and to a degree smoking, so maybe this can happen here too.