I'm not trying to pick sides here, just describing the intention behind the downvote you received from Grumpy. The reward pool that gets distributed each day is shared among everyone, there's a set amount. There are people using paid upvote bots to abuse the system. Bots that sell upvotes to posts close to their payday are considered especially abusive by GrumpyCat, which is why you got that downvote.
If you want to avoid this happening again make sure to only buy upvotes from bots that have a "Max Age" of 3.5 or less listed here: https://steembottracker.com/
Again I'm not picking sides, I'm just saying what happened. Your anger is definitely understandable.
I know what happened, but it's a misuse of the downvote. The downvote is intended for the community to regulate payout to an appropriate value. This was basically @grumpycat saying my content wasn't worth $5. You can't use a downvote the way @grumpycat is using it. It breaks the system equally as bad as voting bots.
Further, from my own investigation I can tell the following:
So I have to disagree with you. I think personally, the best way to keep this from happening again is to get the community to shut down @grumpycat.
I think people look at bots the wrong way. They supplement the system by providing a missing feature. Voting bots basically fix a broken promotion system. Any working feature of a monetary system can be abused though. I get that they can drain the reward pool, but even without voting bots users will find ways to drain the reward pool. You can't blame the feature for what people do. As a result, it gives way to another kind of abuse: downvote abuse which is evident from the existence of @grumpycat. Just like with the @haejin nonsense, it gave way to another community of downvoters to counter the abuse of self-voting.
The trend is to answer abuse with...more abuse. That is NOT an answer.