If you're running the Spotify client, you're using their computer, too, not just your own. You have the right to kick them off of your PC or phone, and they have the right to kick you off of their server. What's the problem with that?
The original comment seems to argue that ad-blockers are morally wrong, which I disagree with. Ad-blockers are a morally neutral technology, even if they hurt some company's bottom line. Companies that dislike this reality can deploy technical countermeasures, like Spotify is doing.