I'm talking about rogue players, or one-man association players, who commit such acts of sabotage without any obvious motivation.
I disagree a little bit on this statement: I think if the motiviation is not obvious, the usual rule of "innocent until proven guilty" applies. In my personal opinion, it's not about about "no obvious motivation", but "obvious motivation to simply being a jerk".
Maybe that is what you meant, maybe not. But in my opinion a player should not be punished just because his intention is not clear (because that also applies to players who just don't know better), but he should only be punished if his intention is clearly "evil" and there is proof for it.
Sabotage, connections, prestige hunters, industry bombing make the competition much more interesting and it's fun.
I agree on that. Rail Nation in general is an extremely cooperative game and quite peaceful, given that you can't really lose anything you earned and any competition is more like a race about who does something best, not about taking something away.
So to keep things interesting, a certain threshold of gameplay-induced friction is a good thing in my opinion. The "salt in the soup", so to speak.
This only gets too much once players use these mechanics for the sole purpose of ruining the fun for others.
Being upset about some things others are doing is part of a competitive game, which Rail Nation still is.
However, doing something ONLY to upset others is not okay.
Distinguishing between the two is not always easy though
About the topic at hand:
The game rules acutally will soon be updated and will include a general rule about fair play that covers...well, pretty much every intentional harmful behavior that is not covered by other rules.
We will also be introducing account bans and increase our efforts concerning multis.
Will this solve all problems? Definitely not. No rule and no punishment in the world can fully prevent harmful behavior, some people simply do it anyway. Punishments are not really that effective at preventing anything.
But it will help.