So it's not necessarily like the content is entirely lost. It was brought up above, but Reddit archives exist.
The alternative is Reddit gets to lock down that data, but because it hasn't gone all the way yet and completely locked it down, everyone is still obligated to let them keep that data? It just doesn't make sense. A user saying, 'fine, but if you're not going to allow open access then I'll stop treating my content like it's open access and I'll remove it' is I think a pretty reasonable response (both for the user and for society). Particularly in the context of the current API decisions, the thing Reddit is doing is closing off access to that data. I mean, if I'm going to treat content on Reddit like it's a public good that I'm morally obligated to provide, then maybe it's bad for a for-profit business that fights with its community to be in charge of that public good. It's not good for the world if a company can say 'look how much value you're giving everyone, you're morally obligated to them to let us keep abusing you.' Users aren't obligated to play into that trap. I also get annoyed when I see missing comments, but I don't think this is a good reading of the situation.