Wow I just wrote a lengthy response here, then clicked reply by accident and lost the whole thing.
I've been getting attacked by these guys too. At first I thought it was my account being specifically targeted because I use boost bots, (a practice I am somewhat on the fence about) but this isn't the case.
I looked into it further, and many people are being victimized by these accounts. It's some kind of mass ring of accounts being used for abuse and nothing more. They clearly don't have an integral understanding of the Steem blockchain, because they are downvoting posts that are past payout, and don't manage their VP in any kind of constructive way.
My initial reaction was anger, but when I figured out what was happening, it became funny to me. These downvotes, as you know, are virtually harmless to your account.
Now, when I make a post, I get the popcorn and can't wait to see how many downvotes I get. It's like a new dynamic that has been added to give some pleasure to my blogging experience. It is more amusing than anything, that people would be willing to waste so much time, because why? They lack creativity? I don't know the answer, but it's beyond sad.
Don't let it get you down. I doubt you will, because you understand just how foolish they are.
This post was downvoted by @trucmipo
I'm sure you probably knew that already though.
Want a good laugh? Go look at his wallet memos....