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Worth noting that most of these criticisms also apply to existential types, which are fairly common in functional languages (e.g. Haskell).

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That's not entirely accurate. Abstract data types (e.g. ML modules) can also be modeled as existential types and don't have the same problems.

I think it's the particular combination of only having nominal typing, only allowing the oo-flavor of data abstraction, and encouraging programming with state and using inheritance for code reuse that leads to the object-spaghetti nonsense in heavily-oo Java/C++ codebases.

I just mean that (at least in Haskell) existential types provide information hiding & combine functions with data. In fact, they're implemented with dynamic dispatch, just as with OOP.

The problem is not that OO languages have these features; the problem is that they lack other features common to functional languages.

Unfamiliar with Haskell. What are existential types.

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