Yes I understand your concern, as I too have been a target of such actions by whales. Nevertheless, I don't consider that out of the rules by any stretch of imagination. Anyone has the right to disagree with the payment at any given moment during the 7 day evaluation period.
It doesn't mean it is a winning strategy for the whale doing it either, and because votes are not really free, it comes with a price. If it is done precariously, it will directly devalue the whale's own investment, as people come vary of either posting quality, or posting at all.
But what I believe will eventually happen whether there are bad whales or not, is that when Hive will come more popular (think 5x, 10x users), the whale vote ceases to count, because of the sheer amount of minnows, little fish and dolphins will outnumber their originally huge votes.
We may still see $300 downvotes, but that will change as volume grows. The whales, orcas and dolphins will likely be busy downvoting normal spam instead.
All true, but when? Hive incl. its predecessor is >5y old. Will the numbers ever be 5x in this decade? Look at the current "growth rate".
The whales will still for a very long time dominate and be able to put off many people.
It's all okay to be pessimistic, but truth be said the whole crypto world is still very young. We've not seen real massive adoption yet. But I believe it will be coming sooner or later and the floodgates will be opened.
The hive account creation process is still a bit of a hassle, and there are also quite a few things we still could improve in the authentication process. So, while we are definitely making progress (Splinterlands et. al.), we are currently not even close to being ready for the big masses yet.