I tend to see it from both sides. In general, I support unions, rights at work and so on as long as its responsibly done. One of the downsides of aggressive capitalism, is under certain circumstances it is very much a race to the bottom for many workers, while those at the top cream off the profits.
The way some of the right wing press demonise much of the public sector as lazy, under-worked, overpaid etc is nothing short of a disgrace. It's not quite as simplistic as saying 'these people do not create growth', because taking education and transport, for example, economic growth would be severely stunted by lack of decent infrastructure and an ignorant population. Some services will never be commercial, and if you are reducing wages at the bottom, and putting people on short term contracts, the safety net is fairly essential in a civilised society. It's not to say some services cannot be in the private sector, but in the case of many (like education and healthcare) that's fine if you can afford to pay for it, or have the opportunities to earn that sort of salary. Most people do not. Moreover as we have seen, healthcare in the private sector, can be far more expensive, especially comparing the US system with the UK one.
Having said all of this, the problem the railways have is one of perception. And indeed, the public perception can be way out of line with the reality. For example, the notion that all trains run late, when 90-95% run on time, a higher percentage than other timetabled transport. The railways are unsafe, when they are now, pretty much the safest form of travel. And the old adage about the railways are simple to run (because the argument goes trains are 1d, road travel is 2d and aviation is 3d) which tends to be the unqualified opinion of people that don't really know what they are talking about. Even enthusiasts have little perception of the dynamic nature of the railway, and how the efforts of so many people doing their job 100% correctly need to interlock together to produce a safe and punctual service. Nor do they appreciate the shear quantity of rules, regulations and safety requirements needed for 100s or 1000s of tons of metal running around on a fixed network at sometimes high speeds.
Nevertheless it can also be argued that most railway staff these days receive fairly good numeration. With most drivers now early 5 times the minimum wage or twice the mean average salary, in some cases on a basic wage. Most customer facing staff like station staff and guards earning fairly good wages as well.
If the RMT/ASLEF have a PR problem it's almost certainly down the willingness to strike coupled with levels of salaries. When someone on 4 or 5 times the minimum wage talks about workers rights, this doesn't tend to go down very well with the majority that are on less wages and are genuinely struggling. As it's been pointed out, the railway is not, for a number of reasons, 100% commercial. Therefore, the argument goes, why should railway people be subsidised more than say teachers, nurses and other essential skilled public workers. And what about those at the bottom, who are struggling to make ends meet? Especially as many of them will be struggling to cope with high rail fares?
Yes, again, there is a perception about the high cost of fares, in some cases this is fair: Such as the cost of walk on travel in the peak, sometimes it is unfair, for example many people compare the cost of petrol v the train fare and wrongly argue the cost of fuel is the real cost of the journey.
Many people also see railway workers in a privileged position. Most workers could not strike in the same way, because they would simply be replaced by a ready stream of labour. This is the case throughout most of the rest of the transport sector.
So why do some enthusiasts have little sympathy? Well surprising as it many seem, some people, especially those in campaign groups trying to protect services, do actually really care about the existence of the network and the success of the railway. In some cases more so than the people whose livelihoods depends on it. The railways attract an enormous amount of loyalty from their followers, to a degree seen little elsewhere.
With high costs (and yes it's not all down to staff costs) currently threatening the existence of sleeper services and intercity service services (north of the border), as many as many schemes such as the northern hub, or reopening schemes, it is of great concern to see the ardent inflexibility of the unions.
The railways are not in a bubble, there are many other competing forms of travel, and many other competing needs for public funds. The unions will simply either price the railway out of the market, or the workers themselves -for example on London underground where it is proposed to replaced all drivers with train attendants similar to the DLR.
The unions may not care about public perception or winning the argument for going on strike. Various people whole work for the industry may tell the public it is none of their business, or they are just jealous. But don't be surprised, in the two way world of the internet that people make their own mind up. If they are not persuaded that workers are worth X most people will generally not be supportive and the unions need to go on a charm offensive to persuade people why they are worth it. Sticking two fingers up regardless and striking in those circumstances rarely wins support.