People don't call suicides selfish because of the methods chosen... otherwise they wouldn't discourage and disparage all of it. A suicide that affects almost nobody is still considered selfish for many reasons, plenty of which aren't valid. People who are suicidal are selfish insofar as they can't tolerate pain for the sake of others further and take what they judge to be the best actions for themselves - usually after many attempts to bear suffering for others, and often while having to live with the idea that they are a burden regardless of whether they're alive or dead. I wish people would reconsider before coming on here and regurgitating those kinds of truisms.
I agree people should seek to minimise their impact on others, but as long as suicide must remain a furtive and difficult act, there are always going to be people who struggle to find a way to do this. And I think loss will always be an emotional response to love; suicide, like any death, will be painful, and right now it is especially so because of what it represents. But I strongly believe that some (not all) of the unique trauma of suicide is induced by the fact that the suicidal must become fugitives to succeed, and what that means for their behaviour, their feelings, their methods, and the circumstances of their death, as well as people's understanding of them and ability to come to terms with it.
I see very few people on here who actively want to cause pain with these methods; there are so many threads on here where it's obvious people are living purely for others or torn up about the impact they will have that it seems preposterous to me to call the suicidal more selfish than anyone else. The harm caused by a suicide is not all harm caused by the individual; it is also harm that was done to the individual to start with. It may be instinctive to recoil from death, but it is also instinctive to make suffering stop.
There is special contempt for people who do it by train due to train driver PTSD - train drivers, at least in my country, are serious agitators for mental health reform, because their suffering is induced by others' suffering. (Of course, it's not just the mentally ill who suicide!) Society has failed train drivers; it denies them rights as workers and alienates them in the same way, it denies them the same treatment other people with PTSD also need (and may even be possible already!), and it fails the mentally ill at every level, then leaves them as the first response to the worst parts of it. Some problems- some intolerable illnesses, some pain, some philosophical issues - are not remediable and not preventable, but those people have no recourse; many situations could be remedied or prevented but are instead exacerbated by people's circumstances.
I feel really, truly bad for train workers - I've read quite a lot about their experiences with suicide - and I think most people do, but I also feel really bad for the people who choose such a method because they feel there is no better way. In the case of an impulsive suicide carried out in blind agony, I feel even worse for them for various reasons. I don't know of anyone who isn't aware that they involve others when they die this way. And finally, if people don't have access to another method that's as reliable as train decapitation or aren't capable of it (whether for psychological reasons or due to their life circumstances), then that's sad too.
I strongly encourage people who are considering this method to do deep reflection within themselves why they can't do something different - if they have particular hangups, maybe those could be overcome. An important part of end of life planning is reflecting on and acknowledging what will likely happen as a result of your actions, and coming to terms with it - including who will be affected and whether one can change that or not. (It's not just the train that can traumatise random people) But also, it's not evil to need a way out of a trap.