Mortgages frequently get bundled up and sold as securities. That's just how it works. Blackrock is one institutional buyer. A mortgage is someone's liability and another's security.
Nothing about "mortgage securities" implies poor lending practices or overleveraging.
https://michael-hudson.com/2019/10/asset-price-inflation-and...
But I admit I'm slightly annoyed by the bad faith in the conversation; that is something I'd expect on Reddit, not HN.
Why make a jump from "You are reminded of this scene" to "You don't understand how the system works"?
Even if we assume that one follows from the other (it doesn't, that's more than disingenuous) - than the way this was phrased is unnecessarily combative, aggressive and derogatory.