The reader of the code should not be forced to stumble over a semantic identity because it is expressed by a syntactic distinction. The reader's focus should not be directed toward the lexical tokens; it should be directed toward the structure, but using square brackets draws the reader's attention unnecessarily to the lexical tokens.

But it is not only about a style. When [x y] means a different thing than (x y) it is a different language construction, with different behavior.