The 7% increase seemingly applies only to an Edinburgh-London ICEC single. ScotRail fares increased by less than 2%, so the TSSA aren't incorrect in who they've chosen to protest against.
Populist campaigns against fare increases don't tend to end up going very well. The result of Sadiq Khan's TfL fares freeze has been to considerably reduce the funding available for long-term improvements. All the hard-pressed commuters are complaining about paying so much for overcrowded, late and cancelled services, yet the effect of freezing those fares is to make it less likely that the services will get any better!
If people want to campaign for something that will actually make public transport better and more affordable then they should be looking at Land Value Taxation. No property magnate has ever decided to charge for the use of the lift in their buildings because it makes them less money, as they fully capture the value of public realm improvements within their building through the rent they charge to tenants. With an LVT, this can happen for the government across the entire country, and so there is a very serious and very plausible case to be made to subsidise public transport fares using the LVT receipts. It shifts the burden of paying for public transport onto the people who actually gain the most from its existence, rather than those who actually use it.
