Be careful about assuming that a throwaway account guarantees anonymity. Based on what HN moderators have said in posts to users misusing throwaway accounts to violate the HN guidelines, they are able to link throwaway accounts to primary accounts. That necessarily implies if HN suffers a severe security breach, all throwaway accounts may be linkable to the main account which would reveal the email address on the main account, if present, and enable researching of the user's identity based on posts on the main account.

That's an option... but if the person behind the throwaway account still receives abuse, it doesn't matter that the abuse didn't come down on their main account. It's still abuse aimed at them as a person, and it still hurts just as much.