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TCP is done via the IO monad and this is an excellent example of what the IO monad is used for---it forces you to realize that there's another layer of (this time quite leaky) abstraction over your potentially simple inner abstraction.

That's a bad example because this code does not use the Monoid abstraction, but rather the Buffer Operations abstraction which does expose performance costs.

>because the "taking away" approach at abstraction also abstracts out some important performance considerations.

a software engineering abstraction which doesn't have clear performance facet is just a bad software engineering abstraction (while, for example, it may be a really good math abstraction).