While this is a reasonable approach, it quickly breaks down when you look at code written by others who do not follow this approach.

When approach X isn't followed, approach X breaks down? True for all approaches, no?

Any language can be written poorly. I don't think any language will ever be able to force good coding style on programmers. Though Haskell comes closer to that impossible goal than many other languages, due to its type system, functional purity, and mandatory indentation.

The difference is that in lisp you cannot chose to not "follow the approach" because the approach is fundamental. So you will never look at anyone else's lisp code and see that they chose not to use parentheses uniformly.

Well, technically it's possible if someone used macros to embed a DSL that is paren free, but it just doesn't happen in the vast majority of cases. Whereas if you try to follow the approach of using parens everywhere in Haskell, the vast majority of other code you attempt to read will still be awkward for you.