I don't disagree with the specific example given, but rather that because those cases exist, we blanket say it's not a bad idea to do so...if that makes sense.

I don't disagree with the specific example given, but rather that because those cases exist, we blanket say it's not a bad idea to do so...if that makes sense. It's why I used 'almost' there. Perhaps it needed to be a little segregated. The initial section is written from the perspective of a library author, asking them not to nuke away types. The example seems more of a middleware/client side thing. More often than not of course it'll make more sense to deal with types at the base layer, and interfaces at the client layers, as that's the point of them, after all.