"And this is precisely what is wrong with dynamically typed languages: rather than affording the freedom to ignore types, they instead impose the bondage of restricting attention to a single type! Every single value has to be a value of that type, you have no choice!"
So, does that mean Lisps are "less powerful" because they tend to use a single data structure (cons) for everything? I think there is a lot of power in simplicity and using a single thing to represent everything else.
Certainly static type systems can let you write different programs than dynamic languages: staticness gives you certain powers that you don't have in dynamic languages. But I would argue that dynamic languages, precisely because they lump everything into a single static type, can have certain benefits as well.
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"For another, you are imposing a serious bit of run-time overhead to represent the class itself (a tag of some sort) and to check and remove and apply the class tag on the value each time it is used."
Indeed. Static languages are well known to be faster than dynamic languages because they have more information at compile-time. Old news. Oh wait, we've developed JIT compilers that can make dynamic languages go astonishingly fast, so the old "performance" argument is a lot weaker nowadays.
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I don't think I'd have a problem with a language that was dynamic by default but lets you specify optional static types. I think that would be the best of both worlds. Unfortunately, the languages that have good static type systems (Haskell, ML, etc.) tend to also emphasize staticness everywhere, requiring you to jump through some hoops to enable dynamicism.
So yeah, I don't think static type systems are evil, I think they're a useful tool, but like all tools, it depends on how you use it. Social norms, idioms, what the language encourages/discourages matter just as much if not more so than the language features themself.
Haskell's been trying to make types optional, which will be interesting to watch. Because even if they loosen their type system their social norms are pretty baked at this point.
Do you have a link for that? I had the impression Haskell already did a pretty good job of supporting untyped code within a module, but if it has something to do with explicit passing of type class instances or untyped module exports, that's pretty interesting. Gradual types would be even more interesting than that.
