I'm not worried about that - it's not my collection, it's Spotify's. I'm merely paying for the unlimited consumption of their collection on demand, not to purchase the songs and have them for life.
It'd be a different story if I expected the songs I listen to on Spotify to be available forever, but I don't, and that's not what I'm paying for.
But I've been there.
When Grooveshark quit -- I was a paying member and had no up-front notice -- I lost my complete library. I've looked into making a back-up before and figured out some technical requirements for that (e.g. I cracked the "encrypted" cached files) but never really got around to it. A list of which songs were in my library and playlists would have been all I needed, but I had no such thing.
Spotify doesn't offer this either. Like with Grooveshark, you can find technical ways of getting around it, but they're not jumping at the opportunity to provide a JSON export that you can import into another music service.
The other side of the coin is that not all music is available. Even now on Spotify, if you enable "show unplayable songs" there are a lot that turn unavailable every month. I don't want to think of which part will not be available at a competitor's.
For all these reasons, I agree with the person you're replying to. But I made the same decision as you -- i.e. I use and pay for Spotify -- because those indie stores just don't have enough music by a long shot to make it worth the trouble. Ideally it would be that way, though.
https://developer.spotify.com/web-api/console/get-current-us...
The hard part is explaining to our mothers that their music app might become unavailable, that they should care about this, and that they should take action to mitigate the effects.
But on the other hand, consumers get locked in all the time, and civilization hasn't collapsed yet.