I know parallel structure makes things look and sound better. But there are sentences that lack symmetry that are still grammatically correct.
I stole an example from a worksheet: The class valued respect, honesty, and being on time in a teacher.
It was marked "incorrect". Why is that "incorrect"? It is correct. It just doesn't comply to a rule I've never heard of until this year. Respect, honesty, and being on time are all nouns. They are each perfectly perfect to be used as direct objects. Why is it suddenly "incorrect" to use a gerund phrase along with plain nouns? Notwithstanding the better flow of "promptness" in place of "being on time", why is it considered "incorrect"? Do teachers take off points for this kind of thing? In my opinion, telling kids they have to use parallel structure is just as stupid as telling them they can't begin sentences with conjunctions.
Why is this a big deal? I'm sure about a hundred years from now, there will be a literary device made up to explain lack of parallel structure. Students will be forced to marvel at the fact that authors chose to deny its existence. Teachers will tell their students that having one odd item out in a list creates emphasis and should be celebrated. Omission of parallel structure will one day become the new polysyndeton.