It's a good point, but you should be accurate - you cannot down vote an account, you can only down vote a post. Whale 3 down votes a post, and this indirectly has negative effect on your rep if and only if the post goes into negative rewards (you can't see this in the steemit.com UI, it just shows zero, but it's recorded).
It's up to Whale 3 to be responsible enough to just counter the rewards they think should be countered. The UI could help with this simple calculation if the Whale is not bothered to do it themselves.
I understand your point. But we should not restrict the possibility of this situation on the blockchain, we should just support positive action and warn of potential common mistakes in the UI (like we do with transfers for example).
I am still new, August 1, 2017. So I am still learning and trying to remember the different terminology used. The person may only be downvoting a Post, but it does affect the posters account and rep. I know because I was downvoted without cause very early on by bernie and his house of 52 cards, (52 down votes), that did affect my reputation. Fortunately I knew about cheetah, steamcleaners, and @timcliff, and they fixed things for me.
But yes when it is strictly a money/reward issue, it is not always the posters fault.