There is absolutely nothing to justify here. Running ad-blockers is perfectly fine in any context whatsoever.
Everybody has the right to control what is displayed on their computer when they browse the Net, and Spotify has the right to cancel free accounts for whatever reason they want to. There is nothing wrong with running adblockers and anti-anti-adblocking scripts, etc., and there is nothing wrong with canceling free Spotify accounts. There is also no cognitive dissonance with running and ad-blocker and being angry when Spotify cancels your free account because of it, it's a perfectly reasonable and consistent attitude.
Everybody has the right to control what is displayed on their computer when they browse the Net, and Spotify has the right to cancel free accounts for whatever reason they want to. There is nothing wrong with running adblockers and anti-anti-adblocking scripts, etc., and there is nothing wrong with canceling free Spotify accounts. There is also no cognitive dissonance with running and ad-blocker and being angry when Spotify cancels your free account because of it, it's a perfectly reasonable and consistent attitude.